Joe Biden has said again and again that he's running for a second term, but there are signs his own voters are ready for a change. A new poll from USAToday found that just 67 percent of Biden's 2020 voters want him to seek re-election.

Biden is also facing a surprisingly robust outsider challenge from Robert F. Kennedy, Jr, who jumped into the Democratic primary on Wednesday. 14 percent of Democrats said they prefer Kennedy over Biden.

Five percent support self-help guru Marianne Williamson, who previously mounted a longshot campaign in 2020. Another 13 percent are unsure.

Replacing Biden

A vaccine skeptic, Kennedy is certainly something of an anachronism in a time when Democrats have embraced COVID shots as a symbol of tribal affiliation.

Kennedy's heterodox viewpoints on COVID vaccines and Ukraine are diametrically opposed to Biden's own, and yet, a non-trivial percentage of Democrats already say they would prefer Kennedy.

He is the choice of a third of dissatisfied Biden voters, and 35 percent who say Biden -- who campaigned as a so-called "moderate" -- has been "too liberal."

“Kennedy, although a long shot at this point, starts in double digits and can’t be ignored," Suffolk County Political Research Center Director David Peleologos told USA Today.

The poll surveyed 600 Biden voters and has a margin of error of 4 percentage points.

Who will replace Biden?

Outside the field of declared Democratic candidates, there have also been rumors about Michelle Obama, whose Oprah-like cult of personality is nothing to sneeze at, and California governor Gavin Newsom (D), who is quite openly auditioning to be president at some time in the future.

Michelle Obama has seemingly closed the door, but Newsom has been crisscrossing the country in a PR campaign heralding California as a shelter of "freedom" from right-wing "authoritarians."

While speculation about Biden's future isn't going anywhere just yet, he has been buoyed by a lack of compelling (and in Obama's case, willing) alternatives and the party's desire to avoid a divisive primary.

Indeed, the Democratic party machine has appeared to mobilize behind him, despite the unenthusiasm of his own base, his consistently underwater approval ratings and his age. Biden would be 86 at the end of a second term.

Trump, the Republican primary favorite, is leading Biden in a RealClearPolitics average of polling data by just under two points.