Robert F Kennedy Jr has said he is suspending his independent run for the US presidency and will back Donald Trump’s campaign.

Mr Kennedy, 70, a Democrat for most of his life and the scion of the powerful Kennedy dynasty said the principles that had led him to leave the party had now compelled him “to throw my support to President 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.

Trump thanked Mr Kennedy, saying: “We just had a very nice endorsement from RFK Jr, and I’ll be talking about that. He’s a great guy, respected by everybody.”

The decision effectively brings to an end a campaign fuelled by Mr Kennedy’s anti-vax views, and coloured by stories of dead bears and brain worms. His polling has slumped from a high of double figures as funds and national coverage dried up.

Members of the Kennedy family, who had opposed his campaign said the decision to endorse Trump was a “betrayal of the values that our father and our family hold most dear. It is a sad ending to a sad story”.

Mr Kennedy said that Trump’s insistence he could end the war in Ukraine by negotiating with Russia “alone would justify my support for his campaign”.

“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 said he would remove his name from 10 states where his presence would be a “spoiler” to Trump’s effort.

Mr Kennedy said he had launched his campaign “as a Democrat, the party of my father, my uncle… the champions of the Constitution” but added he left in October to run as an independent because “it had become the party of war, censorship, corruption, big pharma, big tech, big money”.

He blamed the media and his former party for his decision to suspend his campaign, adding: “In my heart I no longer believe I have a realistic path to victory in the face of systematic censorship”.

In polling before President Joe Biden stepped aside from the race, Mr Kennedy hovered around 14% - 16%, according to the Associated Press. After Kamala Harris became the nominee, his polling average slipped into the single digits.

Before working to elect Trump, Mr Kennedy said he asked to have similar conversations with Ms Harris offering to work with her campaign.

Democrats shrugged off his 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.