Robert F. Kennedy Jr. announced his bid for the presidency Wednesday and became the second nationally recognized candidate to challenge President Joe Biden for the Democratic nomination behind author Marianne Williamson. 

While critics say Kennedy is a long shot to win the nomination, others aren’t so sure. A USA TODAY/Suffolk University poll showed Kennedy took 14% of Biden's 2020 voters at his campaign’s formal launch Wednesday.

Fox News’ Geraldo Rivera argued Kennedy will be much more "formidable" than people think. 

"People are taking him with a grain of salt. But he's got the accent, he's got the nostalgia, he's got the looks," Rivera said Thursday on "The Five." 

Robert F. Kennedy Jr.

BOSTON, MA - APRIL 19: Robert F. Kennedy Jr. officially announces his candidacy for President on April 19, 2023 in Boston, Massachusetts. An outspoken anti-vaccine activist, RFK Jr. joins self-help author Marianne Williamson in the Democratic presidential field of challengers for 2024. (Photo by Scott Eisen/Getty Images) (Scott Eisen/Getty Images)

Rivera added that he favors California Gov. Gavin Newsom to run as a Democratic presidential candidate but ultimately believes President Biden will receive the nomination. He said he expects the 2024 election to be a rematch between Biden and former President Donald Trump. 

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"I still think it's going to be Trump against Biden. But I think that… Robert Kennedy Jr. is going to be a formidable force, a disrupter, at the very least," he explained. 

"Five" co-host Judge Jeanine Pirro said she worked with Kennedy when she was a district attorney and found him to be a "very ethical guy who really believed in what he was doing." 

"He wasn't cheap about politics. He wasn't an easy mark. He was someone who believed in what he believed. And I think it'll be very interesting to watch him," she said.. "I think when you put someone up like him against Joe Biden. and we see he's taken 35% of the Democrats who don't like Joe Biden, who think he's too liberal. And 33% of Joe Biden's people who think that the economy is terrible. I think he has an opportunity."

Pirro added that she thinks some Americans will find Kennedy to be "reminiscent of better times in America."

 "I think it'll be very interesting to watch. He's not about corporate greed. He's not about running around the world and sucking up money with a vacuum cleaner, you know, for the family," she said.

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Kennedy has faced criticism for his anti-vaccine activism, along with his stance against the COVID-19 vaccine. While Kennedy insists that he's not opposed to vaccines and that his sole interest is to make them safer, his Children's Health Defense non-profit has been accused of spreading doubts about the safety of vaccines.

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The 69-year-old nephew of the late President John F. Kennedy, said his mission over the next 18 months will be to "end the corrupt merger of state and corporate power that is threatening now to impose a new kind of corporate feudalism on our country; to commoditize our children, our purple mountains’ majesty; to poison our children and our people with chemicals and pharmaceutical drugs; to strip-mine our assets; to hollow out the middle class and keep us in a constant state of war."

Fox News' Paul Steinhauser and Thomas Phippen contributed to this report