Bill O'Reilly interviews Donald Trump. Fox News/screengrab Fox News host Bill O'Reilly repeatedly challenged a key portion of Donald Trump's immigration agenda during an interview Tuesday night.

The real-estate magnate and Republican presidential candidate recently unveiled his multipart plan to clamp down on illegal immigration.

Among other things, Trump called for ending birthright citizenship, or the right of anyone born in the US to American citizenship.

As O'Reilly pointed out, however, the Constitution's 14th Amendment enshrines birthright citizenship into US law.

"That's not going to happen because the 14th Amendment says if you're born here, you're an American," O'Reilly said. "And you can't kick Americans out. The courts would block you at every turn. You must know all that."

Trump insisted that the Constitution did not grant citizenship to "anchor babies," a pejorative term used to describe the children of people who enter the country illegally with the purpose of having a son or daughter who would then be granted US citizenship.

"Bill, I think you're wrong about the 14th Amendment," Trump said. "And frankly, the whole thing with 'anchor babies' and the concept of 'anchor babies' — I don't think you're right about that."

O'Reilly was incredulous.

"I can quote it!" O'Reilly exclaimed. "You want me to quote you the amendment? If you're born here, you're an American — period! Period!"

The Fox host later added: "You are not going to be able to deport people who have American citizenship now. And the federal courts will never allow mass deportations without due process for each and every one. And do you envision federal police kicking in the doors in barrios around the country, dragging families out?"

Donald Trump v. Mexico NBC Universal/Edgard Garrido/Reuters/Amanda Macias/Business Insider

But Trump, citing unnamed lawyers, held his ground on the citizenship issue.

"Bill, I don't think that they have American citizenship," he said. "And if you speak to some very, very good lawyers — and I know some would disagree, but many of them agree with me — you're going to find they do not have American citizenship. We have to start a process where we take back our country. Our country is going to hell."

For the record, the text of the amendment would seem to favor O'Reilly's interpretation in the dispute. It states: "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States."

O'Reilly also asked Trump whether he would be interested in changing the language of the Constitution to comport with how he sees the citizenship issue.

"It's a long process, and I think it would take too long," Trump responded. "I'd much rather find out whether or not 'anchor babies' are actually citizens, because a lot of people don't think they are."

Trump has based much of his presidential campaign on his opposition to illegal immigration. His heated rhetoric on the issue — especially his accusation that the Mexican government is intentionally sending rapists into the US — touched off a national firestorm after he launched his campaign.

But the controversy has appeared to only fuel his White House bid. Trump has led in almost every recent poll of the Republican primary.

Watch Trump's Fox interview below: