Robert F Kennedy Jr has said he is suspending his independent run for the US presidency and will support Donald Trump.
He insisted he would not drop out, and would keep his name on the ballot in the states where it will not affect the race.
Mr Kennedy, 70, a Democrat for most of his life and the scion of the powerful Kennedy dynasty said: “In my heart I no longer believe I have a realistic path to victory in the face of systematic censorship”.
The announcement came following days of speculation about a potential endorsement of Trump.
The decision effectively brings to an end a campaign fuelled by Mr Kennedy’s anti-vax views, coloured by stories of dead bears and brain-eating worms. His polling has slumped from a high of double figures as funds and national coverage dried up.
At a press conference, Mr Kennedy said polling indicated that staying on the ballot in the battleground states would “likely hand the election over to the Democrats”.
“If you live in a blue state, you can vote for me without harming or helping President Trump or Vice-President Harris and red states, the same will apply,” he said. “I encourage you to vote for me, and if enough of you do vote for me and neither of the major party candidates win 270 votes, which is quite possible.”
Mr Kennedy suggested a 269 to 269 electoral tie is possible with his strategy of staying on the ballot in some states.
He said he would remove his name from 10 states where his presence would be a “spoiler” to Trump’s effort.
Before working to elect Trump, Mr Kennedy said he asked to have similar conversations with Ms Harris.