Former Gov. Andrew M. Cuomo and Zohran Mamdani, a progressive state lawmaker from Queens, will announce strong fund-raising numbers in the New York City mayoral race on Monday as they push to unseat Mayor Eric Adams.

Mr. Mamdani has raised more than $840,000 over the last two months and has more than 16,000 total donors, his campaign said. It is a surprisingly good showing for a candidate who was not well known to New Yorkers until recently, but who has attracted attention for his use of social media and vocal opposition to the Trump administration.

Mr. Mamdani said in an interview that his campaign had momentum because he was focused on addressing the high cost of living in the city.

“We have run a campaign that speaks directly to the working class, and I think that’s resonating,” he said.

The campaign fund-raising deadline on Monday will provide a snapshot of the race roughly 100 days before the Democratic primary in June. Mr. Adams is running for a second term while confronting record-low approval ratings.

Mr. Cuomo, who has led in polls, raised $1.5 million from more than 2,800 donors in 13 days, his campaign said. He expects to receive public matching funds after raising $330,000 in eligible funds from 1,700 donors who live in the city.

His donors include Geoffrey S. Berman, the former United States attorney in Manhattan who was fired by President Trump in 2020; Mr. Cuomo’s former wife, Kerry Kennedy; and Jessica Seinfeld, the cookbook author and wife of the comedian Jerry Seinfeld.

“I’ve been humbled by the depth and breadth of the outpouring of support we’ve received upon entering this race,” Mr. Cuomo said in a statement. “New York is the greatest city in the world, and those who live here deserve a New York that is better, stronger, safer and more affordable than the New York we have today.”

Two other leading Democrats announced their fund-raising totals on Sunday. Brad Lander, the city comptroller, raised $225,000 during the recent filing period that ran from January to March.

“These results show that New Yorkers are hungry to end the Adams-Cuomo nightmare of endless scandal and corruption, and replace it with strong, honest leadership,” he said in a statement.

Adrienne Adams, the City Council speaker who announced her campaign on March 5, raised $128,000 in five days. Her campaign said she had not yet met the threshold for the city’s generous public matching funds program, which awards $8 for every dollar donated by a city resident, up to $250 per person.

Ms. Adams, who is not related to the mayor, visited Bethany Baptist Church in Brooklyn on Sunday and told reporters that she would catch up on fund-raising. She said that even though Mr. Cuomo might be leading in the polls, he had “very high” unfavorable ratings.

She told the congregation that New Yorkers are “tired of the drama” and “tired of the trauma,” an apparent reference to Mr. Adams’s legal and political troubles. Ms. Adams said she had received phone calls from out-of-town relatives asking what was going on in New York.

“We don’t have to continue to be a city of embarrassment,” she said.

Several campaigns have already qualified for public matching funds, including those of Mr. Lander and Mr. Mamdani. A candidate must raise at least $250,000 and receive contributions from at least 1,000 donors who live in the city to qualify.

Mr. Adams, who is facing federal corruption charges, was denied public matching funds in December. The city’s Campaign Finance Board ruled that he was not eligible because of the conduct outlined in his indictment, a decision that prevented him from receiving as much as $4.3 million.

Several of the mayor’s longtime allies have endorsed Mr. Cuomo. Mr. Adams has not begun to campaign seriously, though he insists he is running for re-election.

Mr. Cuomo, who resigned in 2021 after a sexual harassment scandal, is arguing that he is the most experienced candidate and the one who can get things done. He has denied the harassment allegations and challenged his accusers in court.

Mr. Mamdani, who released plans to freeze rents and to make buses free, has risen in the polls. A recent Quinnipiac University poll showed him in third place after Mr. Cuomo and Mr. Adams.

A video of Mr. Mamdani confronting Tom Homan, President Trump’s border czar, in Albany last week went viral. His campaign said he raised nearly $250,000 in the day or so after the video was posted.

Another social media post by Mr. Mamdani was widely skewered for his breach of subway etiquette. A photo showed the candidate placing a large burrito and a side of salsa on a subway seat late one evening while holding a fork and knife over them.

But Mr. Mamdani, who is Muslim, took the ridicule in stride, saying that the photo reflected his busy campaign schedule during Ramadan.

The photo, he said, expressed the reality of “fasting while campaigning and not always having a place to break your fast except the train you’re taking from one event to the next.”

Sean Piccoli contributed reporting.

The family of Brendan Costello gathered in the hospital half-light. He had overcome so much in life, but the profound damage to his brain meant he would never again be Brendan. It was time.

Brendan had spent four months enduring three surgeries and a lengthy rehab after infections further destabilized his damaged spine. He had returned to his apartment on the Upper West Side in late December to begin reclaiming the life he had put on hold — only to go into cardiac arrest three weeks later and lose consciousness forever.

His younger sister, Darlene, stayed by him in the intensive care unit at Mount Sinai Morningside hospital. She made sure that his favorite music streamed nonstop from the portable speaker propped near his bed. The gravelly revelations of Tom Waits. The “ah um” cool of Charles Mingus. The knowing chuckle of New Orleans jazz.

The music captured Brendan: the dark-humored Irish fatalism flecked with hope and wonder. And yes, he used a wheelchair, but woe to anyone who suggested this somehow defined the man.

After tests confirmed no chance of regaining consciousness, a wrenching decision was made. Brendan’s ventilator would be removed at 1 p.m. on Sunday, Jan. 19, five days after his collapse. He was 55.

Now it was Sunday, heavy and gray with dread. Several of Brendan’s closest relatives ringed his bed, including his sister and the aunt and uncle who had raised him. Waits growled, Mingus aahed, the clock ticked.

Then, just two minutes before the appointed hour, as tears dampened cheeks and hands reached for one last squeeze, a nurse stepped into the moment to say that Ms. Costello had a phone call.

What?

A phone call. You have to take it. You HAVE to take it.

The flustered sister left her brother’s room and took the call. Family members watching from a short distance saw her listening, saw her arguing, saw her face contort in disbelief.

Time paused, as all the emotional and spiritual girding to say goodbye gave way to a realization: Of course. Their beloved Brendan — witty, contrarian, compassionate and not-yet-dead Brendan — had other plans.

Of course.

BRENDAN CAME BY his gallows humor honestly. Finding the comedy in tragedy was a coping mechanism, a way of owning the pain, that he shared with his sister.

Their parents were deaf and ultimately incompatible. After their father left the family, their mother — their devoted, hilarious, troubled mother — took her life in the basement of their Brooklyn apartment building. Brendan was 8, Darlene 6.

They went to live with Uncle Marty and Aunt Cathy Costello and their two young daughters in northern Westchester. The couple resolved to raise the four children the same, doing their best to ease the trauma shadowing their nephew and niece.

Young Brendan amused the family with his sardonic asides, did well in class and established a Students for Peace group at Yorktown High School. After college, he took a job writing Wall Street-related news releases that did not suit his talents or interests. He found ways to numb himself.

Late one night in August 1996, a very drunk Brendan fell onto the subway tracks at the Broadway-Lafayette station. The oncoming D train cut his tie just below the knot, in sartorial measure of how close he came to death, and took away his ability to walk. Devastating.

But while rehabbing in a spinal-cord-injury program, he met a man in a wheelchair named Boris, who counseled others about this new chapter in their lives. “Boris told him that when you have an accident like this, you don’t withdraw from the world, you lean into the world,” Marty Costello recalled. “You go out there. And that’s what Brendan did.”

He did so with Brendanesque humor, sometimes wearing a blue Metropolitan Transportation Authority hat or a black T-shirt emblazoned with the orange D train symbol. Just to show there’s no hard feelings, he’d explain.

“If you’ve watched your parents die, or you’ve been run over by a train, you’re at a deeper depth of what’s funny,” his sister said.

Among the many things that bound the two siblings together was the 1986 Jim Jarmusch movie “Down by Law.” Its tragicomic sensibility resonated, as did a line uttered by Roberto Benigni, who played an Italian immigrant struggling to learn English:

“It’s a sad and beautiful world.”

Brendan drove a car, and refused any help getting in or out. Went skydiving. Co-hosted a radio show focused on disability rights and culture. Taught creative writing at the City College of New York. Published pieces in Harper’s, The Village Voice and elsewhere. Became president of the Irish American Writers and Artists organization. Belonged to the St. Pat’s for All group that arranges an annual everybody-welcome parade in Queens. Talked about storytelling with the elementary school students of his cousin Katie Odell, sometimes even letting them sit in his wheelchair.

And he dominated on trivia nights at the Dive 106 bar on the Upper West Side, often helping his team to beat all comers, including, most deliciously, squads of Columbia University students. “He was definitely the MVP of our team,” recalled Leland Elliott, his longtime friend and trivia teammate.

Brendan liked the saxophonic improvisations of Pharoah Sanders, the literary riffs of James Joyce and the Japanese art of Kintsugi, in which a broken thing, such as a shattered piece of pottery, is reassembled with gold or silver lacquer to create something new and wondrous.

He disliked Disney, Apple and, especially, any suggestion that his disability somehow made him inspiring. “He was not somebody who wanted to be seen as a guy in a wheelchair,” his cousin Maryanne Canavan said. “He wanted to be identified by what he brought to the table.”

And what he brought was considerable, she said. “His brain was his superpower.”

THE TELEPHONE CALL that interrupted Brendan’s death was about extending lives, though not his. Just as he had planned.

The caller was from LiveOnNY, the nonprofit organization federally designated to coordinate organ donations in the New York metropolitan area. When a patient who meets specific clinical criteria seems on the cusp of death at a donor hospital, the hospital is required to contact LiveOnNY, which then checks for the person’s name in the database of registered donors.

Years earlier, Brendan had registered while renewing his driver’s license. The caller, a family-support advocate for LiveOnNY, gently explained that this meant he could not be taken off the ventilator. At least not yet.

The news was almost too much to process. Darlene Costello, who moments earlier had been steeling herself to say goodbye to her dear and only sibling, erupted in anger. Why was she only now hearing about this?

Gradually, though, she came to embrace the import, the beauty, of what was unfolding. By late that afternoon, the LiveOnNY representative was at Mount Sinai Morningside, patiently going over the next steps with Ms. Costello and her cousin, Ms. Canavan, both nurse practitioners.

When Ms. Costello learned of the “directed donation” option, in which a family can direct an organ to a specific recipient for a possible match, she felt the gravitational pull of fate. Here was a chance to use a piece from one broken body to make another whole: her mentor and friend, Dr. Sylvio Burcescu.

Dr. Burcescu was a psychiatrist and head of the Mensana Center, the clinic in Westchester where Ms. Costello worked; several of his patients had told her that his counsel had saved their lives. Now a rare and debilitating kidney disease had upended his own life, and he was on the registry for a transplant.

“I was completely incapacitated by dialysis,” Dr. Burcescu, 62, said, recalling the exhaustion, the pain and the extreme limitations on his liquid intake. “A very bad situation.”

When Ms. Costello called, he braced for bad news about her brother. Instead, he said, she sounded excited, even upbeat, and asked a question that took his breath: Do you want one of Brendan’s kidneys?

As she explained what had unfolded, the doctor struggled to corral his many emotions: sadness, embarrassment, humility, gratitude. Finally, he said: It would be an honor.

So much had suddenly changed, and so much still had to fall into place. The chance of a match between Brendan and Dr. Burcescu was slim; of the 2,052 kidney transplants that LiveOnNY has facilitated over the last three years, only about 50 resulted from directed donations.

“The sun, moon and stars have to line up,” said Leonard Achan, the president and chief executive officer of LiveOnNY. And if they didn’t, he said, the organ would instead be offered to the most compatible person at the top of the national waiting list.

A battery of testing and measuring and analyzing determined that here was a rare, against-the-odds match. “A miracle, really,” Mr. Achan said. “A case of somebody saying, ‘I know someone.’ And it actually works out.”

THE NURSE AT Mount Sinai Morningside hospital has never seen so many visitors. A few dozen, easily, with some crammed in a certain patient’s room and the rest spilling into the seventh-floor hall of the intensive care unit.

But after several years of nursing experience, Cornelius Sublette knows to keep his “ICU mind.” Pay close attention to his patient’s oxygenation, blood pressure and comfort, and be ready to meet every possible need of the grieving family.

His mantra: “To offer self.”

It is Wednesday, Jan. 22, three days after the revelation of Brendan’s last wish had postponed his death. He lies in Room 24, as music triumphs over the mechanical beep of reality. Fiona Apple sings of seeing not just the crescent but the whole of the moon, while Sting summons a haunting Irish air, hundreds of years old, about a gallant darling hero.

People take turns donning masks, gloves and yellow isolation gowns before entering the small room to say a word, a prayer, a goodbye. Hospital guidelines allow for only two visitors at a time, but accommodations have been made for the crush of love.

The air changes when the operating room on the third floor calls to say that everything is set; it is time, once again. Mr. Sublette kicks the red lever at the base of Brendan’s bed, releasing the brake.

With the help of another nurse, he guides the bed out of Room 24 and into the hall. Along the walls, family members, friends and hospital workers stand at attention, in somber respect for someone who, in his imminent death, is about to give life. It is a ritual called the honor walk.

Steering the bed, the two nurses in their teal scrubs take care to walk at a slow, even pace. Brendan’s relatives fall in behind, one by one, as his music washes over them.

The procession turns left at the intensive care unit’s small command center and moves toward the glowing-red exit sign above the automatic doors. Beyond is a steel-silver elevator that will take Brendan four floors down to the operating room.

There, in a little while, his ventilator will be disconnected, and his breathing will end. His left kidney will go to his sister’s friend, Dr. Burcescu, who will soon drink as much water as he wants. His right kidney will go to a man in Pennsylvania, his lungs to a woman in Tennessee. He will donate, too, his ever-searching eyes.

In a couple of weeks, there will be a funeral Mass at the Roman Catholic Church of the Ascension, his old parish on the Upper West Side. Hundreds will attend. A holy jazz will play.

All that will come in the days ahead. But for now, Louis Armstrong is singing full-throated about the march of saints as Brendan Thomas Costello Jr. leads a procession, sacred and slow, through this sad and beautiful world.

Audio produced by Parin Behrooz.

Crowds of masked student protesters raging against the war in Gaza filled the Columbia University lawns last spring, while counterprotesters and journalists surrounded the tent city that had been erected there.

One man stood out.

He was Mahmoud Khalil, a graduate student in his 20s, older than most of the students around him. Mr. Khalil, a Syrian immigrant of Palestinian descent, quickly emerged as a vocal and measured leader during rallies and sit-ins, doing on-camera interviews with the media in a zip-up sweater.

And he was unmasked. Many other international students wore masks and kept to the background of the protests, for fear of being singled out and losing their visas.

His wife worried. “We’ve talked about the mask thing,” Noor Abdalla, a 28-year-old dentist from the Midwest, said in an interview last week. “He always tells me, ‘What I am doing wrong that I need to be covering my face for?’”

Mr. Khalil was a negotiator on behalf of Columbia University Apartheid Divest, the main coalition of protesting student groups, and one with its own spectrum of attitudes toward violence and dark rhetoric.

His decision to quite literally be the face of a deeply divisive movement would have huge consequences for Mr. Khalil. He was called out by critics by name on social media, and on March 8, seven weeks after the inauguration of Donald Trump, federal agents arrived at his door. He was swiftly taken to a detention center in Louisiana, where he is still being held for what officials have described, without providing details, as leading activities aligned with Hamas, an allegation he has denied.

Mr. Khalil’s friends and family have expressed outrage at his detention and possible deportation. But they also say they are not surprised by his activism in a movement that he was born into, nor his relatively calm presence amid a swarm of noise.

As he moved through the world, Mr. Khalil could often come across as the adult in the room. And to one who had known him as an office mate in an earlier time, his role in front of microphones and wielding a bullhorn came unexpected.

“He’s very sort of mild mannered,” said Andrew Waller, a former colleague who worked with Mr. Khalil in Beirut at the British diplomatic office for Syria. “Seeing him in more of a sort of leadership or spokesperson role, I guess was a surprise.”

Mr. Khalil arrived at Columbia University at the end of a long and winding journey. His Palestinian origin story was written and ended before he was born.

His grandparents were from a village near Tiberias, a city on the western shore of the Sea of Galilee in Palestine before it became part of the state of Israel. They were forced to flee in 1948 during the wars preceding Israel’s establishment, Mr. Khalil has said, settling with other members of their large family in southern Damascus in Syria, in a Palestinian refugee enclave. It was there that Mr. Khalil was born in 1995.

In the early 2010s, he fled the Syrian conflict to Lebanon, where he arrived alone and broke. He worked in construction to make enough money to pursue an education, according to his friend Ahmad Berro, who met Mr. Khalil while the two were studying at Lebanese American University. Mr. Khalil graduated in 2018 with a degree in computer science.

While in Lebanon, Mr. Khalil worked with Jusoor, a Syrian American educational nonprofit. There, in 2016, he met the woman who would become his wife, a U.S. citizen of Syrian descent.

In 2018, he began working on programs related to Syria for the British diplomatic office in Beirut. He eventually oversaw a scholarship program for foreign students to study in Britain. His work was informed by his personal experiences of fleeing Syria and his opposition to the government there, Mr. Waller, his former colleague, said.

After about four years, Mr. Khalil set his sights on the United States and applied to a few graduate schools. He hoped to be accepted at one in particular, Columbia University and its School of International and Public Affairs.

He was accepted and enrolled in January 2023.

He saw it as a huge win, not only for himself, but for his fellow refugees, said Lauren Bohn, a journalist who met Mr. Khalil in Beirut and spent time with him after his admission to Columbia. “He said, ‘This will really help me serve all the others who aren’t going to be able to get this chance.’”

He had been at the university for some nine months when everything changed on Oct. 7, 2023.

A campus in turmoil

Students at Columbia turned out for protests immediately after Hamas’s attacks on Israel. Some were quiet calls for peace, others more raucous. Pro-Palestinian and anti-Israel chants rang through the campus, rattling many Jewish students.

Mr. Khalil was on the front lines with Palestinian activists, bracing for a counterattack from Israel that was imminent. In a video from Oct. 12, five days after the attacks, he is seen atop another person’s shoulders, shouting “Free Palestine!” into a bullhorn.

Months of protests followed. Then, in April 2024, pro-Palestinian students established an encampment at the center of campus. They demanded that the university divest from what they called “all economic and academic stakes in Israel,” including Columbia’s dual-degree partnership with Tel Aviv University.

The rows of tents pitched on Columbia’s iconic, grassy lawns inspired similar protests at universities across the United States. They became a flashpoint after Columbia’s president called the New York City police to campus, leading to the arrests of more than 100 people. As the protests intensified, some Jewish students complained about feeling unsafe. Some heard anti-Zionist chants as threatening to them personally. Those accounts reached Congress, where Republicans derided the protests as antisemitic and Columbia as out of control.

When negotiations began between the protesters and the university, Mr. Khalil emerged as a lead spokesman for the students. The two sides met day and night. A Columbia administrator who negotiated with him described Mr. Khalil as thoughtful, passionate and principled, sometimes to the point of rigidity. He got his back up when he felt he wasn’t being taken seriously. Mr. Khalil was also a face of the protesters for the news media, where he was sharply critical of the university, stepping confidently up to banks of microphones where reporters from CNN, Spectrum News NY1, The Associated Press and The New York Times and elsewhere recorded him confronting the school that had brought him to New York.

“It’s very clear the university does not want to criticize Israel in any way,” Mr. Khalil told a gaggle of journalists gathered near the encampment last spring.

On another occasion, at a discussion sponsored by the coalition of student protesters, he remarked that whether Palestinian resistance was peaceful or armed, “Israel and their propaganda always find something to attack.” He added, “They — we — have tried armed resistance, which is, again, legitimate under international law.” But Israel calls it terrorism, he said.

Those comments were highlighted as justifying terrorism by pro-Israel activists on a webpage about Mr. Khalil that had been compiled by Canary Mission, a group that says it fights hatred of Jews on college campuses and that pro-Palestinian protesters say has doxxed them.

Still, Mr. Khalil repeatedly told friends, as he had his wife, that he saw no reason to wear a mask. What were they going to do to me? he asked.

Once, when the number of tents rose to more than 100, including on a second lawn near the School of Journalism, administrators turned to Mr. Khalil. They made him an offer: Remove about 20 tents, they said, and we’ll ensure that the university’s trustees continue to discuss your demands.

Mr. Khalil countered, agreeing to remove a few less than the administrators wanted, according to one administrator present at those talks, who spoke on condition of anonymity to discuss private university negotiations.

Within minutes, 17 tents vanished and the second lawn was emptied. This response burnished Mr. Khalil’s reputation as a good-faith, if demanding, negotiator.

Other times, he stood fast. Late in the protests, when the university offered concessions and the threat of the police arriving to clear out demonstrators was looming, Mr. Khalil pushed back. We don’t want your concessions. The police? Let them come.

Then they did.

New protests, new president

After a faction of protesters took over Hamilton Hall, a campus building, on April 30, barricading doors and trapping custodians inside, scores of police officers descended on the university. They arrested dozens of pro-Palestinian demonstrators and cleared the hall.

Mr. Khalil was not accused of being in the hall. He had been suspended by the university just before the building takeover, accused of refusing to leave the encampment, along with many other pro-Palestinian activists, and then was quickly reinstated. But there were no more negotiations, and the protests ended for a time.

Columbia slowly ceased being the global flashpoint for campus unrest. Mr. Khalil focused on finishing his courses and looking for work after graduation.

He and Ms. Abdalla married, and he obtained a green card, giving him permanent residency in the United States.

Last summer, the couple learned that they were having a baby. Mr. Khalil was excited, his friends said, getting their apartment ready even as the couple looked ahead toward moving after he earned his degree.

“He did everything, basically,” Ms. Abdalla, now eight months pregnant, said. “He did all the cooking, he did all the cleaning. He did the laundry. He wouldn’t let me touch anything.”

He finished his coursework for his master’s degree from the School of International and Public Affairs in December. But he remained aware of protests still bubbling up at Columbia and at Barnard College, across Broadway.

In January, protesters stormed into a Columbia classroom, and two Barnard students were later expelled that month for their roles that day. It was a flashback to the turmoil of the previous spring. While Mr. Khalil was not present, he was soon drawn back in.

Days later, President Trump, newly inaugurated, issued an executive order promising to combat antisemitism and prosecute or “remove” perpetrators of such views.

The same night, an X account of a Zionist group singled out Mr. Khalil. It accused him, without evidence, of saying that “Zionists don’t deserve to live,” and said that the federal Immigration and Customs Enforcement agency had his home address. “He’s on our deport list,” the post said.

It included a video of Mr. Khalil speaking in a CNN interview, during which he made no such statement. Mr. Khalil has said he had “unequivocally” never spoken those words — another student had, and was expelled.

Mr. Khalil saw himself and other student protesters as victims of doxxing, finding their personal information spread on social media. On Jan. 31, he emailed Columbia administrators asking for protection for international students, such as himself, who he said were facing “severe and pervasive doxxing, discriminatory harassment and very possibly deportation.” A Columbia spokeswoman declined to comment on communications from Mr. Khalil.

Jasmine Sarryeh, a close friend, tried to allay his concerns and told him he would never be deported. Now she feels like she let him down.

“I didn’t think to expect that this would happen,” she said in a recent interview.

‘Suspected Foreign National’

On March 5, in response to the expulsion of the Barnard students in January, protesters dressed in kaffiyehs and wearing masks descended upon the college’s library. It was a Wednesday, and Mr. Khalil turned from his baby preparations and attended as well, maskless again.

It was the beginning of a four-day stretch that would end with Mr. Khalil in federal detention.

Videos on social media depict him at the library holding a megaphone — and, at one point, using it to amplify the Barnard president, who is speaking over a cellphone. When the protesters are asked if they want to speak with the president, Laura Rosenbury, Mr. Khalil gives them an encouraging thumbs up. They respond in unison: “Yes!”

Critics of the protests immediately began posting videos and images of Mr. Khalil on X, calling him out by name.

One post included an image of his face circled in red with the label “Suspected Foreign National.”

Then, Shai Davidai, an Israeli Jew and Columbia professor banned from campus in October after he was accused of harassing employees, reposted that image and tagged another X account. It belonged to Marco Rubio, the secretary of state, who had just posted a threat to deport Hamas supporters.

“Illegally taking over a college in which you are not even enrolled and distributing terrorist propaganda should be a deportable offense, no?” Mr. Davidai wrote.

Separately, Shirion Collective, a group that says it exposes antisemitism, has said that it sent the Department of Homeland Security a legal memorandum advising the “detention and removal” of Mr. Khalil.

Mr. Khalil saw some of the posts online and panicked. He was being singled out for deportation directly to the very official with the power to set that process in motion.

On Friday, March 7, he again wrote to Columbia administrators and described a “vicious, coordinated and dehumanizing doxxing campaign” against him.

“I haven’t been able to sleep, fearing that ICE or a dangerous individual might come to my home,” he wrote.

That fear would be realized the next day.

‘Let’s bring him in.’

Mr. Khalil and his wife were out with friends on Saturday night, March 8. When they returned to their Columbia apartment, a man in plain clothes pushed into the lobby behind them. Ms. Abdalla felt her husband tense.

“He knew something was wrong,” she said.

I’m with the police, the man said. You have to come with us. More officers arrived in the lobby. Ms. Abdalla hurried up to their apartment to get her husband’s green card. She reminded the officers that he was a permanent citizen.

“‘This guy has a green card,’” she heard the officer say on his phone. “And then the guy on the phone with him told him, ‘Let’s bring him in anyway.’”

In a video recording of the arrest, she is heard asking the officers repeatedly to identify themselves and to specify what charges her husband was facing. She rushes after the officers into the street as they ignore her questions.

It remains unclear what exactly Mr. Khalil is believed to have done. He is accused by the White House and others of organizing protests, such as the one in the Barnard library, where participants distributed fliers promoting Hamas. A flier that was shown in online postings from the library said it had been produced by the “Hamas Media Office.” It was titled “Our Narrative” and listed Hamas’s code name for the Oct. 7 attacks, with an image of fighters standing on a tank. It is unclear whether Mr. Khalil knew the fliers were there.

“I can wholeheartedly say that I know that he did not touch those fliers,” said Mr. Khalil’s friend, Maryam Alwan. “But just because he had his face out, people are trying to pin everything on him.”

His lawyers also denied that he had distributed the fliers at Barnard.

Mr. Waller, his former colleague in Lebanon, said the depictions of Mr. Khalil that he had seen in the news media did not line up with the friend he knew.

“The idea that he’s somehow a political extremist or a sympathizer with terrorist groups or whatever just sounds totally outlandish,” he said. “If you know him and you know his character, it just feels like a sort of obvious smear.”

There are circumstances in which permanent residency status in the United States can be revoked — if, for example, the resident is convicted of a crime. But Mr. Khalil has not been accused of any crime. Instead, Secretary Rubio has cited a little-used statute as the rationale for Mr. Khalil’s detention. The law says that the government can initiate deportation proceedings against anyone whose presence in the country is deemed adversarial to the United States’ foreign policy interests.

Mr. Davidai, the professor who tweeted the photo at Secretary Rubio, said in an interview that he believed Mr. Khalil was entitled to due process under the law. But, he added, it does not so much matter whether Mr. Khalil personally handled fliers promoting terrorists, if the group he represented did.

“When you lead an organization, you are accountable for your organization’s actions,” Mr. Davidai said. “When you lead an organization that openly and proudly supports a U.S. designated terrorist organization, you are accountable to the spreading of propaganda.”

Mr. Khalil has said he was never the planner and leader of the pro-Palestinian protests; he has consistently described himself as a spokesman and negotiator for a coalition of student groups.

Resolving this was not the job of the agents who came to his lobby that Saturday night. They handcuffed Mr. Khalil, led him to a car waiting outside and drove him away.

Katherine Rosman, Sharon Otterman, Jonah E. Bromwich and Michael LaForgia contributed reporting. Kirsten Noyes contributed research.