The longshot presidential campaign that Robert F. Kennedy Jr. launched 16 months ago from Boston’s Park Plaza hotel effectively came to an end Friday afternoon in Arizona, when the third-party candidate announced he’s now backing Republican nominee Donald Trump.

Kennedy said he would withdraw his name from the ballot “in about 10 battleground states where my presence would be a spoiler.”

He said he worried remaining in the race in those key states could “hand the election over to the Democrats with whom I disagree on the most existential issues: censorship, war and chronic disease.”

“It is with a sense of victory, and not defeat, that I am suspending my campaign activities,” Kennedy said in a livestreamed address. “Not only did we do the impossible by collecting a million signatures, we changed the national political conversation forever.”

Kennedy’s name will still be on the ballot in many states. He emphasized in his address that he was not officially ending his bid, and many voters will still be able to cast their ballot for him in November.

Also in his speech, Kennedy highlighted hopes to fold his views around health, food production and chronic disease into a potential second Trump administration.

UMass Amherst political scientist Tatishe Nteta said obtaining that kind of platform has been one goal of the Kennedy campaign, since independent candidates traditionally face “infinitesimally low” odds of winning the White House.

“If coalition with Trump potentially leads to some influential position in the administration, in some ways that leads to success for the Kennedy campaign,” said Nteta, a professor and director of the UMass Poll.

Nteta told GBH News the move is a positive one for Trump’s campaign, but it may not translate into a huge shift in votes for Trump. A national poll UMass conducted in July found that if Kennedy voters had to choose between Trump and Vice President Kamala Harris, 29% would pick Trump and 26% Harris.

A longtime environmental lawyer, Kennedy has become known for his anti-vaccine activism and willingness to embrace conspiracy theories. He is the nephew of former President John F. Kennedy Jr. and son of Robert F. Kennedy, who served as U.S. attorney general in his brother’s administration and was assassinated during his own presidential bid.

Though Robert F. Kennedy Jr. often invoked his political lineage during the campaign, other members of the Kennedy family distanced themselves from him. More than a dozen Kennedy relatives endorsed President Joe Biden this spring, when he was still seeking reelection.

Five of Kennedy’s siblings signed onto a statement Friday afternoon reiterating their support for the Democratic ticket.

“We want an America filled with hope and bound together by a shared vision of a brighter future, a future defined by individual freedom, economic promise, and national pride,” the statement said. “We believe in Harris and Walz. Our brother Bobby’s decision to endorse Trump today is a betrayal of the values that our father and our family hold most dear. It is a sad ending to a sad story.”

Even in Massachusetts, where the family name has cache, Kennedy polled in the single-digits.

A May survey from UMass and WCVB asked Bay State residents to describe him in a single word. Nteta said many of the replies were negative. The most common response was “nut.”

“In the state in which the Kennedy name dominates and the Kennedy family dominates as well, or at least has a positive history, this description of one of the progeny of the Kennedys is going to be problematic for the ability of RFK to win Massachusetts and to win the presidency,” Nteta said.

He said dynamics shifted for Kennedy after Biden dropped out of the race and Harris emerged as the Democrats’ candidate.

“One of the central takeaways from any third-party candidate, and Kennedy is included, is that most third-party supporters are disaffected voters. They view both the Democratic and the Republican candidate in a sort of negative light,” Nteta said. “When Biden was at the top of the ticket earlier this year, we [saw] high levels of dissatisfaction among voters for a rematch of the 2020 election. But with the change from Biden to Harris, those disaffected voters seemingly have been moving towards Harris and away from third-party candidates like Kennedy, like Cornel West and others.”