Judge Andrew Napolitano said Wednesday on "Outnumbered" that Congress cannot stop the child of an undocumented parent from becoming a legal American citizen.

President Trump is arguing that birthright citizenship shouldn't apply to babies of parents in the United States illegally.

He said in an interview with Axios that he intends to restrict birthright citizenship by way of an executive order.

Napolitano, though, said the only way that birthright citizenship can be altered is through a Constitutional amendment.

"Once here, the baby born is an American citizen," he said.

Too Shocking for Google? Marsha Blackburn Ad Flagged Over Footage of Left-Wing Protesters

Trump tweeted on Wednesday that the "so-called" policy "will be ended one way or the other" and is costing the country billions.

Napolitano said that the debate over birthright citizenship isn't serious, disagreeing with Jonathan Turley's argument

He added that the phrase "and subject to the jurisdiction thereof" was added to the 14th Amendment to ensure that the child of anyone not subject to American jurisdiction isn't a legal citizen.

"Illegals can be prosecuted, illegals can go to court and sue. They are as 'subject to the jurisdiction' as those of us who were born here."

Napolitano said the 14th Amendment has been interpreted by courts to mean the same thing for 150 years.

Watch the discussion above.

'We're About 150 Years Late': Turley Says 'There's a Good Debate' Over Birthright Citizenship

Graham: If You're a Republican and Not Excited to Vote, 'You're Legally Dead'

McCarthy on Birthright Citizenship: Trump 'Right on Substance' But Executive Order Won't Work