US President Donald Trump has promoted a false theory that Kamala Harris is not eligible to serve as Joe Biden's Vice President because her immigrant parents were not citizens at the time of her birth, but the case of an Irish girl born in 1819 is crucial in debunking the false theory. 

Trump said that he had heard Harris wasn't eligible to serve as Vice President after claims circulated on social media and he even went as far as saying that John Eastman, the conservative lawyer behind the viral claim, was "a very highly qualified, very talented lawyer." 

He said that he wasn't sure if Eastman was right and said that he presumed that the Democrats would have checked Harris's eligibility. 

"I would have assumed the Democrats would have checked that out before she gets chosen to run for vice president." 

The President then said that people were suggesting that Harris wasn't fit to serve because she wasn't born in the country.

A reporter quickly told him that Harris was born in California. 

Harris's parents, however, were not American citizens at the time of her birth - her father is a Jamaican immigrant while her mother immigrated from India - and Trump appeared to reference this at the White House press conference. 

The President has a long history of opposing "Anchor Babies" - a term given by Trump and his supporters to the sons and daughters of immigrant parents who automatically claim birthright citizenship. 

Trump has long sought to abolish birthright citizenship, but the case of Julia Lynch in 1844 set a precedent that has enshrined birthright citizenship in the US Constitution. 

Julia Lynch, the daughter of Irish immigrants, gained notoriety as the first "anchor baby" when she attempted to enter America in 1834 to collect her uncle's inheritance. 

Read more: America’s first “anchor baby” was an Irish girl named Julia Lynch (VIDEO)

Lynch had been born in New York to Irish parents 14 years previously before her parents moved back to Ireland shortly after her birth. 

Lynch's uncle, Thomas Lynch, had died in New York in 1833 and left behind a sizeable inheritance. 

To be eligible to collect her uncle's inheritance, Julia Lynch had to be considered an American citizen and she had never been officially naturalized, even though she had been born in the United States. 

Judge Lewis Sandford, who presided over Lynch's case, determined that the 14-year-old was, and always had been, an American citizen. 

"It is, therefore, the law of the United States that children born here are citizens, without any regard to the political condition or allegiance of their parents," Sandford said. 

More than 30 years later, under the influence of Lynch's case and other similar cases, birthright citizenship became protected in the US Constitution under the 14th Amendment.

It means that claims that Kamala Harris isn't fit to serve as Vice President are simply outrageous nonsense. 

The theory, referenced by Trump and retweeted by his Senior Legal Advisor Jenna Ellis, echoes previous attempts to undermine Barack Obama's presidency by falsely claiming he wasn't born in the country. 

Those false claims, also endorsed by Trump's campaign when the President demanded to see Obama's birth certificate, were also unfounded and unsubstantiated. 

Trump has since grudgingly conceded that Barack Obama was, in fact, born in the United States. 

Read more: Donald Trump makes an idiot of himself over Obama birther issue

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