A black sheep of one of the nation’s most prominent political families announced his unlikely candidacy for president on Wednesday, in a bid that is a long shot to take him to Washington but could nonetheless inject chaos into the Democratic primary.

Robert F. Kennedy Jr. — the nephew of former president John F. Kennedy and son of former senator Robert F. Kennedy, and a leading crusader of the antivaccine movement — told a crowd of several hundred at the Boston Park Plaza Hotel that it’s time for the nation to return “a Kennedy Democrat’’ to the White House, which he pledged, if victorious, to rid of the “corrupt merger of state and corporate power.’’

In a speech that stretched on for nearly two hours, Kennedy leaned hard into his family legacy, spoke at length about his record of environmental activism, and railed against the COVID-era restrictions he blames for economic distress and worse.

Once well-known for his work as an environmental lawyer, Kennedy, 69, has in recent years made more headlines for espousing conspiracy theories, including the thoroughly debunked claim that childhood vaccines are linked to autism.

In denouncing COVID-19 public health measures such as vaccine mandates and mask requirements, he has more than once in recent years invoked the Holocaust, including when he lamented in 2022 that “even in Hitler’s Germany, you could cross the Alps to Switzerland. You could hide in an attic like Anne Frank did.’’ (He later apologized.)

Those comments and others earned him condemnation from other family members and even his wife, the actress Cheryl Hines.

In anticipation of his presidential bid, Kerry Kennedy, his sister, said in a statement earlier this month that “I love my brother Bobby, but I do not share or endorse his opinions on many issues.’’

Kennedy alluded to those divisions in his speech Wednesday, joking that “most American families, they never have any differences with each other.’’ But he also sought to cloak himself in his family’s legacy of statesmanship. Before the speeches began, family photos featuring famous faces showed on loop on screens at the front of the ballroom, and supporters waved red, white, and blue signs booming, “I’m a Kennedy Democrat.’’

A substantial chunk of Kennedy’s speech was devoted to family lore, including his recollection of the thousands of people who lined the train tracks when he traveled with the body of his slain father to Washington, D.C., in June 1968.

But despite that storied history, “there is no clamoring in the Democratic Party for this Kennedy,’’ said Erin O’Brien, a political science professor at University of Massachusetts Boston. “If your last name is Kennedy, running as a Democrat makes historical sense and the most sense — all in the context of this candidacy making no sense.’’

“I would bet everything I own that this has zero electoral impact,’’ O’Brien added.

Indeed, the views that have deepened rifts with his relatives also seem unlikely to endear Kennedy to Democratic voters. COVID-19 vaccines are not only an unambiguous public health triumph but also a popular innovation among Democrats, who are more likely to have been vaccinated than Republicans, data show.

In his lengthy and wide-ranging address, Kennedy seemed to acknowledge that these realities make his run challenging, joking about the high tally of “skeletons in my closet’’ and acknowledging he is “not an ideal presidential candidate for normal times.’’

“In normal circumstances I would not do this,’’ he said. “But these are not normal circumstances. I am watching my country being stolen from me.’’

Emma Platoff can be reached at emma.platoff@globe.com. Follow her on Twitter @emmaplatoff.