GLENDALE: Robert F. Kennedy Jr, scion of America's storied political clan, suspended his long-shot presidential bid on Friday and endorsed Donald Trump, injecting new uncertainty into the White House race.

"I no longer believe that I have a realistic path of electoral victory," Kennedy, an anti-vaccine activist and conspiracy theorist who was polling in the low single digits, said at a press conference in swing state Arizona.

Kennedy, 70, condemned the selection of Vice President Kamala Harris as the Democratic standard-bearer without a primary contest and cited a long list of grievances against his former party that he said had led him to now "throw my support to president Trump."

Kennedy failed to get on the ballot in even half of the 50 US states and his independent candidacy featured a number of bizarre twists -- including his claim to be suffering from a parasitic brain worm and a story about dumping a dead bear cub in Central Park.

It also drew the opposition of most of his famous family.

"Our brother Bobby's decision to endorse Trump today is a betrayal of the values that our father and our family hold most dear," five of his siblings said in a joint statement in which they endorsed Harris. "It is a sad ending to a sad story."

Kennedy's withdrawal came a day after the surging Harris gave an electrifying speech at the Democratic National Convention in Chicago, accepting the party's nomination and embarking on the final 10-week sprint to election day on November 5.

'He's a great guy'

Analysts are mixed on the effect Kennedy's exit will have on the presidential race and how much of his supporters will gravitate to Trump or Harris.

However, in a very tight contest, it is possible that even a few thousand votes in a crucial swing state could determine who wins the White House, as both sides chase the sliver of undecideds.

At a Trump rally in Glendale there were repeated references by speakers including Charlie Kirk and Kari Lake to a MAGA movement they said welcomes all, including disaffected Democrats.

Within minutes of taking the stage, Trump was welcoming Kennedy to the microphone, accompanied by pyrotechnics and "My Hero" by the Foo Fighters.

A slightly uncomfortable-looking Kennedy told the cheering crowd he wanted to work with a future President Trump to get "the chemicals out of our food."

Trump heaped praise on Kennedy, saying they would "fight together to defeat the corrupt political establishment and return control of this country to the people."

He also used Kennedy's appearance to announce the formation of what he called an "independent presidential commission on assassination attempts."

"They will be tasked with releasing all of the remaining documents pertaining to the assassination of President John F. Kennedy," he said.

The 1963 killing of the president -- Robert F Kennedy Jr's uncle -- continues to fascinate much of the country, and remains the subject of myriad conspiracy theories.

Kennedy's voters are also in the sights of the Harris campaign, with campaign chair Jen O'Malley Dillon saying the Democrat "wants to earn your support."

"Even if we do not agree on every issue, Kamala Harris knows there is more that unites us than divides us," she said.

Neck and neck 

Harris and Trump are neck and neck in the polls less than three weeks before their September 10 debate in Philadelphia.

Harris, 59, a former senator from California and prosecutor, left the Democratic convention in Chicago with momentum, having outraised Trump and erased the polling leads he enjoyed before she replaced President Joe Biden on the Democratic ticket last month.

In just a month, Harris, the first Black woman to top a major party ticket, has raised a record-breaking half-billion dollars.

Her campaign got another potential boost Friday when Federal Reserve chair Jerome Powell said the "time has come" for an interest rate cut -- a move that will lower mortgage costs.

'Unserious'

Trump, 78, has been mobilizing his right-wing base with apocalyptic warnings about migrant criminals and painting a dark picture of a country in "decline" that only he can save.

Harris and her Democrats have been reaching toward the center.

Party strategists spent the week in Chicago showcasing a parade of anti-Trump Republicans, including ex-cabinet officials, a small-town mayor and a former statewide office holder.

"If you vote for Kamala Harris in 2024, you're not a Democrat, you're a patriot," former Georgia lieutenant governor Geoff Duncan said.

While they previously characterized Trump as a demagogue, Democrats have instead begun making fun of the Republican nominee in a manner designed to belittle him and dent his aura of invincibility.

Harris, for her part, called him an "unserious" person.