I no longer believe that I have a viable path to victory, Kennedy said at the press conference in Phoenix, Arizona, where he announced his decision.
Kennedy said, among other things, referring to his own opinion polls, that his participation in the presidential election could harm Trump and help the Democratic candidate Kamala Harris.
He added that he would not formally withdraw his candidacy, but would remain on the ballot in states where his participation would not risk affecting the outcome. In addition to Pennsylvania, he has taken steps to be removed from the ballots in Arizona.
The decision to withdraw follows talks with Donald Trump over the past few weeks, Kennedy said.
Trump speaks
A few hours after Kennedy's press conference, Trump will hold a campaign rally in nearby Glendale, a meeting that has led to increased speculation about a withdrawal from Kennedy's side.
Trump's campaign has hinted that a "special guest" will appear at the rally, without answering whether this guest could be Kennedy.
Trump praised Kennedy on CNN last week, calling him a "brilliant guy". He also opened up to giving Kennedy a role in his new government if he drops out and supports Trump.
In August opinion polls, Kennedy had support of around five percent.
The siblings: "Betrayal"
Kennedy's withdrawal may possibly benefit Trump on the margin, American media writes, as Kennedy is more popular among Republican-minded voters.
Most of the Kennedy family has opposed his candidacy, instead expressing support for the Democrats, the party of his murdered father Robert F "Bobby" Kennedy.
The decision to back Trump "is a betrayal of the values that our father and our family hold dearest", writes his sister Kerry Kennedy and four other siblings in a statement.
"It's a sad end to a sad story", they add.
Kennedy is the son of Robert F "Bobby" Kennedy, senator and justice minister who ran for president when he was murdered in 1968. He is also the nephew of President John F Kennedy, who was shot dead in Dallas in 1963.
Kennedy – a lawyer, professor, and author by day – initially entered the 2024 presidential race as a Democrat but left the party to become an independent candidate.
As an environmental lawyer, he has several times taken on large pharmaceutical and oil companies and won notable cases on environmental pollution.
In recent years, however, the focus has increasingly shifted to Kennedy's statements on vaccines and his advocacy of conspiracy theories.
