Hours after announcing the endorsement in a press conference, Kennedy joined Trump on Friday 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 November 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.

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.