Independent US presidential candidate Robert F. Kennedy Jr. abandoned his campaign on Friday and endorsed Republican Donald Trump, ending a run that he began as a Democrat trading on one of the most famous names in American politics.

Hours after announcing the endorsement in a press conference, Kennedy joined Trump at a campaign event in Arizona, where the crowd cheered the independent loudly.

"His candidacy has inspired millions and millions of Americans, raised critical issues that have been too long ignored in this country," Trump said of Kennedy.

Strategists said it was unclear whether Kennedy's endorsement would help Trump, who is in a tight contest with Democratic Vice President Kamala Harris ahead of the Nov. 5 election.

Kennedy, 70, told a news conference earlier that he met with Trump and his aides several times and learned they agreed on issues like border security, free speech and ending wars.

"There are still many issues and approaches on which we continue to have very serious differences. But we are aligned on other key issues," he told reporters.

He reiterated much of that when he joined Trump at the Arizona rally and repeated positions on his core issues of combating chronic illness and ridding the environment and food supply of hazardous chemicals.

With Kennedy on stage, the former president said that if he regained the White House, he would create a presidential commission on assassination attempts and release files related to the assassination of President John F. Kennedy in 1963.

Robert Kennedy, known by his initials RFK Jr., said he would remove his name from ballots in 10 battleground states likely to determine the outcome of the election and remain as a candidate in other states.

An environmental lawyer, anti-vaccine activist and son and nephew of two titans of Democratic politics who were assassinated during the turbulent 1960s, Kennedy entered the race in April 2023 as a challenger to President Joe Biden for the Democratic nomination.

With some voters at the time turned off by both the aging Biden and the legally embattled Trump, interest in Kennedy soared. He later decided to run as an independent, and a November 2023 Reuters/Ipsos poll showed Kennedy with 20% support in a three-way race with Biden and Trump.

He ran a high-profile advertisement during the February 2024 Super Bowl that invoked his father, U.S. Senator Robert F. Kennedy, and uncle, President Kennedy, and drew outrage from much of his high-profile family.

His sister Kerry Kennedy said on Friday that his decision to endorse Trump betrayed the family's values. "It is a sad ending to a sad story," she said on social media.

For a time, both the Biden and Trump campaigns showed signs they were worried that Kennedy could draw enough support to change the election outcome.

But as the race changed quickly in the last two months -- with Trump surviving an assassination attempt and the 81-year-old Biden bowing to pressure from his own party and passing the campaign torch to Harris -- voter interest in Kennedy waned.

An Ipsos poll this month showed his national support had fallen to 4%, a tiny number but one that could still be meaningful in a tight race such as the current Trump-Harris matchup.

Democrats shrugged off Friday's announcement.

"Donald Trump isn’t earning an endorsement that’s going to help build support, he’s inheriting the baggage of a failed fringe candidate. Good riddance," Democratic National Committee senior adviser Mary Beth Cahill said in a statement.

Drexel University political science professor William Rosenberg said the move was unlikely to have an impact on the race, given Kennedy's low poll numbers.

Trump pollster Tony Fabrizio argued that more of Kennedy's supporters would back Trump than Harris in battleground states. "This is good news for President Trump and his campaign," he wrote in a memo.

In exchange for endorsing Trump, Kennedy was hoping for a job in a potential Trump administration, a super PAC supporting Kennedy told Reuters on Wednesday.

Kennedy painted himself as a political outsider. He told Reuters in an interview in March that if elected president he would repeal many provisions of Biden's signature Inflation Reduction Act and would seek to close down the southern border to immigrants entering the U.S. illegally. He also offered staunch support for Israel.

Bear, brain worms

Kennedy said this month in a video posted online that he dumped a dead bear in New York City's Central Park a decade ago and staged it to look like a bike had hit it. He proclaimed he had "so many skeletons in my closet" after a former family babysitter accused him of sexual assault. He denied that a picture of him posing with the barbecued carcass of a large animal belonged to a canine.

And then there was the brain worm. Kennedy's campaign confirmed that he had a parasite in his brain more than a decade ago, but has since fully recovered, drawing widespread ridicule.