By Jarrett Renshaw

PHILADELPHIA (Reuters) -Robert F. Kennedy Jr, an environmental lawyer, anti-vaccine activist and son of the former senator, announced on Monday in Philadelphia that he is dropping his Democratic Party bid for president and will run as an independent.

Kennedy sought to cast himself as a unifier and a voice for voters who are fed up with the United States' partisan divides and vitriol, calling them a hurdle for improving the country.

"People stop me everywhere, in airports and hotels and on the street. And they remind me that this country is ready for a history making change ... I'm here today I'm here to declare myself an independent candidate," Kennedy told a crowd of several hundred gathered in front of the National Constitution Center.

American Values 2024, a super-PAC supporting the candidate, has raised $17 million, co-founder Tony Lyons told Reuters at the event, an increase from about $10 million reported in July. He expects $10 million more after the announcement, he said.

Kennedy's announcement complicates a 2024 race heading toward a rematch between President Joe Biden, a Democrat, and former President Donald Trump, the Republican frontrunner in opinion polls. Both remain unpopular with a large sections of the American public.

Kennedy's siblings - Kerry Kennedy, Rory Kennedy and Joseph Kennedy II - on Monday denounced their brother's candidacy in a statement: "Bobby might share the same name as our father, but he does not share the same values, vision or judgment. Today's announcement is deeply saddening for us."

COULD DRAW VOTES FROM BOTH BIDEN AND TRUMP

Kennedy's combination of deep-pocketed backers, famous name and lack of enthusiasm for Trump or Biden, could give his campaign heft, political strategists said.

He could draw the support of about one in seven U.S. voters, according to a Reuters/Ipsos poll released last week, and pull votes from both Biden and Trump. Third party candidates have failed to win in U.S presidential races, but they have played a major role in who does win.

At a Democratic National Committee gathering in St Louis last week, party faithful were both dismissive and concerned.

"Outside of his name, what does he have? He’s an anathema to his family’s legacy. It’s sort of a disgrace,” said Ken Martin, head of Minnesota’s Democratic Party.

Others expressed caution.

"It’s going to be a very, very close race, so every vote counts. We can’t go into this election with rose-colored glasses,” said Charles Wilson, chair of Washington DC’s Democratic Party.

Many Democrats also point to the challenges independent candidates face getting on general election ballots in many states, such as collecting tens of thousands of signatures.

"It is a huge challenge. The two major parties have made it impossible for third-party candidates to get on the ballot," said Diane Sare, an independent candidate for U.S. Senate in New York who attended the Kennedy announcement.

The Trump campaign and the Republican National Committee did not return requests for comment.

Brian Noble is a 42-year-old Army veteran who served during the Iraq war who has grown cynical of U.S. politics. He voted for President Barack Obama in 2008, but has sat out each consecutive election. He is so engaged in a Kennedy run that he drove from Alabama to attend the announcement on Monday.

“I believe he’s a truth teller,” Noble said.

(Reporting by Jarrett Renshaw and Heather Timmons; editing by Grant McCool)