President Trump said on Thursday that the U.S. would begin testing nuclear weapons again for the first time in decades.

“We’ve halted many years ago, but with others doing testing I think it’s appropriate to do so,” the president told reporters aboard Air Force One.

Experts say that the resumption of testing would be a major escalation and could upend the nuclear balance of power.

“I think a decision to resume nuclear testing would be extremely dangerous and would do more to benefit our adversaries than the United States,” said Corey Hinderstein, vice president for studies at the Carnegie Endowment for Nuclear Peace.

Here’s what a test would involve, and why the president might be calling for one now.

There’s currently only one place America could test a nuke — near Las Vegas, Nevada

The Nevada National Security Site, approximately 60 miles northwest of Las Vegas, is currently the only place where America could test a nuclear weapon, says Robert Peters, a senior research fellow for strategic deterrence at the Heritage Foundation.

The Nevada site is around 1,300 square miles in size, larger than the state of Rhode Island. Starting in the 1950s, scientists conducted atmospheric nuclear tests at the site, but from 1962 to 1992, testing was done underground.

Today, testing would likely be done in “a complex of deep underground mineshafts,” Peters said.

Scientists dig a deep shaft either directly below ground or into the side of a mountain. They then put a nuclear device in a chamber at the end of the shaft and seal it up. The detonation is contained by the rock, reducing the risk of atmospheric fallout.

Although underground testing is far safer than atmospheric testing, it still carries risks, said Hinderstein. In the past, some radioactive fallout has leaked from test shafts. Additionally, the test could shake buildings as far away as Las Vegas, and Hinderstein said some of the newer buildings in Vegas could even be at risk of damage.

“All of these big highrises — including Stratosphere, including the Trump Hotel,” she said. “They’re not designed for massive, significant seismic activity.”

America’s last test in Nevada was over 30 years ago

At the end of the Cold War, the nation’s major nuclear powers declared a voluntary moratorium on nuclear testing. Russia, then the Soviet Union, tested its last nuclear weapon in 1990, the U.S. conducted its final test in 1992, and China conducted its last test in 1996.

The U.S. conducted hundreds of underground tests in Nevada. Each massive explosion created a subsidence crater visible at the surface.

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The voluntary test moratorium has been in place as part of an effort to maintain nuclear stability. The U.S currently uses scientific experiments and supercomputer simulations to make sure its bombs still work.

Last year, NPR was one of a handful of organizations granted rare access to the top-secret underground tunnels where the tests take place. Scientists working in the tunnels said they were confident they could continue to ensure the safety of America’s nuclear weapons without testing.

Although a full-scale nuclear detonation would be “complementary” to current experiments, “our assessment is that there are no system questions that would be answered by a test, that would be worth the expense and the effort and the time,” Don Haynes, a nuclear weapons scientist from Los Alamos National Laboratory told NPR as they walked through the tunnels.

Indeed Hinderstein says, preparing for a nuclear test is no small matter. While a basic demonstration test could be done in approximately 18 months. Conducting a test that would produce scientifically useful data would likely take years.

In this photo taken from video distributed by Russian Defense Ministry Press Service on Wednesday, Oct. 22, 2025, the crew of the Bryansk nuclear submarine of the Russian navy prepares to conduct a practice launch of an intercontinental ballistic missile during the drills of Russia’s nuclear forces.

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Trump’s announcement is likely reacting to some recent tests by Russia

On Sunday, Russia announced it had conducted a successful test of a new nuclear-powered cruise missile. Then on Wednesday President Vladimir Putin announced the successful test of another doomsday weapon — a nuclear-powered underwater drone, which Russia says can be used to attack coastal cities.

Trump never called out Russia by name, but he did suggest recent testing was behind the announcement. “I see them testing,” he said aboard Air Force One, “and I say, ‘Well if they’re going to test I guess we have to test.’”

While testing nuclear-powered weapons is not the same as testing nuclear weapons themselves, Russia’s tests are highly provocative. They come just months before the expiration of the last nuclear treaty between the U.S. and Russia, designed to put limits on their arsenals.

The back-and-forth has all the hallmarks of the start of an arms race, noted Jon Wolfsthal, the director of global risk at the Federation for American Scientists.

“We saw this play out throughout the Cold War through nuclear testing, nuclear deployments, nuclear investments,” he said.

Many experts warn that now is not the time to resume nuclear testing

Hinderstein, who served as a deputy administrator of the National Nuclear Security Administration, the agency responsible for America’s nuclear weapons, from 2021-2024, said that a decision to resume testing would not be in America’s interests.

At the end of the Cold War, the U.S. had conducted more than a thousand nuclear tests — far more than any other nation (China, by comparison had conducted just 45).

Other nations, “have more to gain by resuming nuclear testing than the United States does,” she said.

Testing would likely be expensive adds Paul Dean, vice president for global nuclear policy at the Nuclear Threat Initiative. “The cost estimates I’ve seen have been at around, ballpark, $140 million per test,” he said.

“It’s not necessary to conduct a nuclear explosive test right now” agreed Robert Peters of the Heritage Foundation. But he added. “But there very well be compelling reasons to test in the coming months and years. That’s how bad things are getting.”

Since Sept. 2, the U.S. military has been attacking boats in the Caribbean Sea and eastern Pacific Ocean that the Trump administration says are smuggling drugs, killing dozens of people. A broad range of legal specialists on the use of lethal force have said that the strikes are illegal extrajudicial killings because the military is not permitted to deliberately target civilians — even suspected criminals — who do not pose an imminent threat of violence.

This is a drastic departure from past practice. The Coast Guard, with assistance from the Navy, has typically treated maritime drug smuggling in the Caribbean as a law enforcement problem, interdicting boats and arresting people for prosecution if suspicions of illicit cargo turn out to be correct.

The White House has said the killings are lawful. It cited a notice to Congress in which the administration said President Trump “determined” that the United States is in a formal armed conflict with drug cartels and that crews of drug-running boats are “combatants.” It has not supplied a legal theory to bridge the conceptual gulf between drug trafficking and an armed attack.

The New York Times is tracking the boat strikes as details become available. The strike locations and casualty figures are drawn from postings by Mr. Trump or Defense Secretary Pete Hegseth, and have not been independently confirmed by The Times.

PEORIA, Ill. (AP) — A jury on Wednesday convicted an Illinois sheriff’s deputy of second-degree murder, a lesser charge, in the shooting death of Sonya Massey, a Black woman who called 911 to report a suspected prowler.

Watch Massey’s family and supporters speak after the verdict in the video player above.

Sean Grayson could be sentenced to up to 20 years in prison or even probation. The jury did not convict him of first-degree murder, a crime that carries a sentence of 45 years to life.

Massey’s supporters were angered by the result. Her father, James Wilburn, called it a “miscarriage of justice.”

WATCH: Activists demand reform and justice after deputy shoots and kills Sonya Massey in her home

“She called for help and she was murdered in her own home. … Second-degree murder — that is not right. That is not justice for anybody’s family,” Teresa Haley, a civil rights activist in Springfield, Illinois, told reporters outside the courthouse.

Grayson and another deputy arrived at Massey’s home in Springfield early on July 6, 2024, after she reported a prowler. He shot the 36-year-old woman after confronting her about how she was handling a pot of hot water on the stove.

Grayson and his attorneys argued that he fired his gun in fear that Massey would scald him with hot water.

Massey’s killing raised new questions about U.S. law enforcement shootings of Black people in their homes, and prompted a change in Illinois law requiring fuller transparency on the background of candidates for law enforcement jobs.

Grayson, 31, was charged with first-degree murder, but the jury was given the option of considering second-degree murder, which can apply when a defendant faces a “serious provocation” or believes their action is justified even if that belief is unreasonable. He will be sentenced on Jan. 29.

State’s Attorney John Milhiser declined to comment as he left the courtroom. He was repeatedly praised by Massey’s supporters for pursuing a trial that was moved 75 miles (120.7 kilometers) north to the Peoria County courthouse because of intense publicity in Springfield.

Defense attorney Daniel Fultz declined comment after the verdict.

“While we believe Grayson’s actions deserved a first-degree conviction, today’s verdict is still a measure of justice for Sonya Massey,” the family’s attorneys, Ben Crump and Antonio Romanucci, said after the seven-day trial.

Body camera video recorded by another Sangamon County sheriff’s deputy at the scene, Dawson Farley, was a key part of the prosecution’s case. It showed Massey, who struggled with mental health issues, telling the officers, “Don’t hurt me,” and repeating, “Please God.”

When the deputies entered the house, Grayson saw the pot on the stove and ordered Massey to move it. Massey jumped up to retrieve the pot, and she and Grayson joked about how he said he was backing off from the “hot, steaming water.” Massey then replied, “I rebuke you in the name of Jesus.”

Both Grayson and Farley drew their pistols and yelled at Massey to put the pot down. Grayson told investigators he thought her “rebuke” meant she intended to kill him and, in the following commotion, fired three shots, striking Massey just below the eye.

Farley testified that Massey didn’t say or do anything that caused him to view her as a threat. But under cross-examination, he acknowledged that he initially reported to investigators that he feared for his safety because of the hot water. Farley did not fire his weapon and was not charged.

Grayson, who was subsequently fired, testified in his own defense. He told jurors he noticed the bottom of the pot was red and he believed Massey planned to throw the water at him. He said Massey’s words felt like a threat and that he drew his gun because officers are trained to use force to get compliance.

“She done. You can go get it, but that’s a head shot,” Grayson told Farley after the shooting. “There’s nothing you can do, man.”

Grayson relented moments later and went to get his kit while Farley found dish towels to apply pressure to the head wound. When Grayson returned, Farley told him his help wasn’t necessary, so he threw his kit on the floor and said, “I’m not even gonna waste my med stuff then.”

Massey’s death forced the early retirement of the sheriff who hired Grayson and generated a U.S. Justice Department inquiry. The federal probe was resolved with Sangamon County Sheriff’s Department’s agreement to fortify training, particularly de-escalation practices; develop a program in which mental health professionals can respond to emergency calls; and to generate data on use-of-force incidents.

Massey’s family settled a lawsuit against the county for $10 million, and state lawmakers changed Illinois law to require fuller transparency on the background of candidates for law enforcement jobs.