Donald Trump attacked Elizabeth Warren, the first major Democrat candidate to declare for the 2020 presidential race, saying voters should "ask her psychiatrist" if she could win.
Ms Warren,69, the US senator from Massachusetts, announced her White House run on New Year’s Eve, saying she would "fight all the way" against Mr Trump.
The two politicians have previously had high profile disagreements. Mr Trump’s nickname for Ms Warren is "Pocahontas" over her controversial claims of Native American ancestry.
Asked whether he thinks Ms Warren believes she can beat him, Mr Trump told Fox News; "Well, that I don’t know. You’d have to ask her psychiatrist."
Referring to her Native American ancestry claims Mr Trump told the interviewer: "I think you have more [Native American ancestry] than she does, and maybe I do too, and I have nothing.
"So, we’ll see how she does. I wish her well, I hope she does well, I’d love to run against her."
Mr Trump’s aides have suggested he would be delighted if Ms Warren, an outspoken critic of Wall Street, won the Democrat nomination,.
The president believes he can beat her more easily than some of the other two dozen possible Democrat candidates.
AP
Ms Warren already has a staff of 70, and $12.5 million in campaign money, giving her a head start on Democrat rivals.
During her campaign Americans will come to know her life story, which includes growing up in Oklahoma, going to work as a waitress aged 13 when her father suffered a heart attack, before becoming a school teacher, a law professor at Harvard, and then a firebrand liberal senator.
Nate Silver, the election analyst, said Ms Warren could become the standard bearer for the Democrat left, adding: "She’s always raised a ton of money. Voters know what she stands for."
On New Year’s Eve, Ms Warren hosted a livestream event from her kitchen on Instagram, the social media platform.
She cracked open a beer, cooked, introduced her dog Bailey, and took questions from her followers.
The candidate said she was planning to watch Casablanca on New Year’s Eve because the film "fills me with hope".
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