Trump wants to send US citizens to foreign prisons. Legal experts say he can't.

The Trump administration has deported hundreds of migrants it alleges are MS-13 gang members -- calling them "terrorists" -- to El Salvador's notorious CECOT mega-prison.

Could American citizens convicted of violent crimes be next?

"If it's a homegrown criminal, I have no problem," President Donald Trump told reporters in the Oval Office on Monday during his meeting with Salvadoran President Nayib Bukele.

"If we can do that, that's good. And I'm talking about violent people. I'm talking about really bad people. Really bad people. Every bit as bad as the ones coming in."

Before reporters entered the room, Trump even suggested to Bukele he should build more prisons because the mega-prison isn't "big enough" to hold "the homegrowns" he wants to send from the U.S.

"We're studying the laws right now," Trump said, after earlier saying they "always have to obey the law."

He made a similar comment about sending Americans to foreign prisons in February, saying back then as well that the laws would be need to be checked.

Several legal experts told ABC News any such scenario would be unconstitutional.

"I don't think that any president who understands the rule of law or who respects the constitutional democracy that we live in would even think in these terms," said David Leopold, an attorney and former president of the American Immigration Lawyers Association.

"The United States is the home of United States citizens. And citizens cannot be deported, period," Leopold said.

"There are numerous constitutional provisions that bar the president and the attorney general from sending American criminals to prisons in other nations," said Michael Gerhardt, a constitutional law professor at the University of North Carolina.

Several administration officials have been pressed to elaborate on what legal grounds they believe would allow them to do this. So far, they've sidestepped.

"Well, Jesse, these are Americans who he is saying who have committed the most heinous crimes in our country. And crime is going to decrease dramatically because he has given us a directive to make America safe again," Attorney General Pam Bondi, who Trump specifically said was looking into the issue, told Fox News' "Jesse Watters Primetime" on Monday night.

"These people need to be locked up as long as they can, as long as the law allows. We're not going to let them go anywhere. And if we have to build more prisons in our country, we will do it," Bondi said, notably mentioning sending Americans to prisons in the U.S.

White House press secretary Karoline Leavitt was asked on Tuesday if deporting American citizens to Central American prisons is legal or if the administration would have to change the law.

"Well, it's another question that the president has raised," Leavitt responded. "It's a legal question that the president is looking into."

Trump and other officials said they'd deport American criminals who commit "egregious" crimes. Trump on Monday cited criminals who "push people into subways" or "hit elderly ladies on the back of the head."

"Of course, we have the right as a government to incarcerate people who are a danger to society, even to execute people who are danger to society, but they're Americans, they remain here. That's the baseline right of citizenship, and always has been," said Amanda Frost, a professor at the University of Virginia School of Law.

Any effort to deport an American citizen to a prison in El Salvador (its CECOT prison has been criticized for alleged human rights abuses) or elsewhere would likely be a violation of the Eighth Amendment, which prohibits cruel and unusual punishment, Frost said.

One potential loophole could be for the Trump administration to try to target naturalized U.S. citizens, who can lose their immigration status if they've committed treason or falsified information during their naturalization process. But those instances are rare.

"If someone’s a naturalized citizen, there could be an effort to denaturalize that person and deport them," Frost said. "But then it would have to be that they committed some sort of fraud or error in their naturalization process. An unrelated crime could not be the basis for denaturalizing and deporting somebody."

Still, experts were alarmed by Trump's comments on wanting to send American citizens to foreign prisons -- especially as the legal battle regarding Kilmar Abrego Garcia continues to play out.

Abrego Garcia is being held at CECOT after being wrongfully deported by the Trump administration last month. Trump and other officials claim he is a MS-13 gang member, though the administration has provided little evidence of that in court.

The Supreme Court has ordered the Trump administration to "facilitate" Abrego Garcia's return to the U.S. and say he was deported illegally. Bondi on Monday said it was "up to El Salvador" to return him, and Salvadoran President Bukele said he wouldn't do so.

"That is chilling," Frost said, "because if that's their view, then assuming they can manage to get people out of the country, they could then throw up their hands and say, 'We can do nothing about it.'"

ABC News Senior Political Correspondent Rachel Scott on Tuesday asked Trump's "border czar" Tom Homan if he believed it was illegal for Trump to send Americans to an El Salvador prison. Homan said he hasn't talked to the president yet.

"The notion is just so absurd," Leopold, the former president of American Immigration Lawyers Association, said. "If it wasn't so terrifying that a sitting president of the United States so loosely uses rhetoric about deporting United States citizens, it would be laughable."