The Trump administration invoked an obscure statute over the weekend in moving to deport Mahmoud Khalil, a permanent legal resident of the United States who recently graduated from Columbia University, where he helped lead campus protests against high civilian casualties in Gaza during Israel’s campaign against Hamas.

Mr. Khalil was arrested by immigration officers on Saturday and then sent to a detention center in Louisiana. On Monday, a federal judge in New York, Jesse M. Furman, ordered the federal government not to deport Mr. Khalil while he reviewed a petition challenging the legality of the detention.

Here’s what to know about the administration’s attempt to deport Mr. Khalil.

Who is the Columbia graduate?

Mr. Khalil, 30, earned a master’s degree from Columbia’s School of International and Public Affairs in December. He has Palestinian heritage and is married to an American citizen who is eight months pregnant.

At Columbia last spring, Mr. Khali assumed a major role in student-led protests on campus against Israel’s war efforts in Gaza. He described his position as a negotiator and spokesman for Columbia University Apartheid Divest, a pro-Palestinian group.

What’s the legal basis for his arrest?

The Trump administration did not publicly lay out the legal authority for the arrest. But two people with knowledge of the matter, who spoke on the condition of anonymity to discuss sensitive internal deliberations, said Secretary of State Marco Rubio relied on a provision of the Immigration and Nationality Act of 1952 that gives him sweeping power to expel foreigners.

The provision says that any “alien whose presence or activities in the United States the Secretary of State has reasonable ground to believe would have potentially serious adverse foreign policy consequences for the United States is deportable.”

What is Mr. Khalil being accused of?

That is not very clear.

Mr. Rubio reposted a Homeland Security Department statement that accused Mr. Khalil of having “led activities aligned to Hamas.” But officials have not accused him of having any contact with the terrorist group, taking direction from it or providing material support to it.

Rather, the administration’s rationale is that the protests that Mr. Khalil played a key part in were antisemitic and created a hostile environment for Jewish students at Columbia, the people with knowledge of the matter said. Mr. Rubio’s argument, they said, is that the United States’ foreign policy includes combating antisemitism across the globe and that Mr. Khali’s residency in the nation undermines that policy objective.

Could this happen to more visa or green card holders?

President Trump said Mr. Khalil’s case was “the first arrest of many to come.”

But a lawful permanent resident, or green card holder, is protected by the Constitution, which includes First Amendment free-speech rights and Fifth Amendment due-process rights. The Trump administration’s efforts to deport Mr. Khalil under the I.N.A. provision are likely to face a constitutional challenge, several legal experts said.

What happens next?

There is little precedent for deporting a legal permanent resident based on the provision of the 1952 law that gives the State Secretary a broad power to do so on foreign-policy grounds.

A lawyer for Mr. Khalil, Amy Greer, said her client would “vigorously” challenge the Trump administration’s actions in court. On Monday, Judge Furman, of the Federal District Court in Manhattan, scheduled a hearing for two days later after barring the Trump administration from deporting Mr. Khalil “to preserve the court’s jurisdiction.”

What has President Trump said about pro-Palestinian protesters?

Since 2023, Mr. Trump has repeatedly vowed to revoke visas of international students who participate in pro-Palestinian protests and criticize Israel’s war efforts.

At a rally in Iowa on Oct. 16, 2023, Mr. Trump declared that “in the wake of the attacks on Israel, Americans have been disgusted to see the open support for terrorists among the legions of foreign nationals on college campuses. They’re teaching your children hate.”

He added: “Under the Trump administration, we will revoke the student visas of radical, anti-American and antisemitic foreigners at our colleges and universities, and we will send them straight back home.”

At a speech in Las Vegas on Oct. 28 of that year, Mr. Trump said that “we’ll terminate the visas of all of those Hamas sympathizers, and we’ll get them off our college campuses, out of our cities and get them the hell out of our country.” And at a Nov. 8, 2023, campaign stop in Florida, he said he would “quickly cancel the student visas of all Hamas sympathizers on college campuses, which have been infested with radicalism.”