Robert F. Kennedy Jr. withdrew from the ballot in Arizona, as both he and Donald Trump were set to appear miles apart in the Phoenix area on Friday amid speculation that Kennedy could drop his independent presidential bid and endorse the Republican nominee.

Kennedy is scheduled to speak at 2 p.m. ET in Phoenix "about the present historical moment and his path forward," according to his campaign. Hours later, Trump will hold a rally in neighbouring Glendale.

Trump said Thursday that "no plans have been made" for Kennedy to appear with him on Friday, but later in the evening the former president's campaign made an unusual announcement, teasing that he would be joined by "a special guest" at his Glendale event.

Kennedy's Arizona withdrawal, confirmed by a spokesperson for the secretary of state, came less than a week after Kennedy submitted well more than the required number of signatures to appear on the ballot.

But on Thursday, Kennedy, his running mate Nicole Shanahan and all of their electors submitted notarized letters dated that day, withdrawing from the race in the state.

Arizona swung to the Democrats in the 2020 presidential election by just over 10,000 votes.

Stalled campaign, ballot access issues

Kennedy, the son of former attorney general Robert F. Kennedy and a nephew of former president John F. Kennedy, hasn't disclosed the reason for his Friday remarks, but they come as his campaign's momentum has slipped.

Kennedy Jr. first entered the 2024 presidential race as a Democrat but left the party last fall to run as an independent. He built an unusually strong base for a third-party bid, fuelled in part by anti-establishment voters and vaccine skeptics who have followed his anti-vaccine work since the COVID-19 pandemic. But he has since faced strained campaign finances and mounting legal challenges, including a recent ruling from a New York judge that he should not appear on the ballot in the state because he listed a "sham" address on nominating petitions.

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Recent polls put Kennedy's support in the mid-single digits. And it's unclear if he'd get even that in a general election, since third-party candidates frequently don't live up to their early poll numbers when voters actually cast their ballots.

There's some evidence that Kennedy's staying in the race would hurt Trump more than Harris. According to a July AP-NORC poll, Republicans were significantly more likely than Democrats to have a favourable view of Kennedy. As well, when given a second choice of candidate, Trump had an advantage of 15 percentage points among Kennedy supporters.

But presently, it's a hypothetical question in many states as Kennedy has only officially gained ballot access in about half of all states. Democrats have mounted legal challenges in expected battleground states like Georgia and Pennsylvania, citing the address issue that invalidated his New York bid.

Running mate floats idea of Trump support

Last month, during the Republican National Convention, Kennedy's son posted and then quickly deleted a video showing a phone call between Kennedy and Trump, in which the former president appeared to try to talk Kennedy into siding with him.

Trump told CNN on Tuesday that he would "love" an endorsement from Kennedy, whom he called a "brilliant guy." He also said he would "certainly" be open to Kennedy playing a role in his administration if Kennedy drops out and endorses him.

While Trump was buoyed after last month's Republican convention in Milwaukee, the Democrats have been energized by a change at the top of their ticket, when the party coalesced in supporting Vice-President Kamala Harris after President Joe Biden announced he would not run for a second term. Democrats also hope the choice of running mate Tim Walz, the governor of Minnesota, will resonate as they seek to produce strong results in Midwestern states.

Shanahan also openly suggested on a podcast this week that his campaign might "walk away right now and join forces with Donald Trump." While she clarified that she is not personally in talks with Trump, she entertained the idea that Kennedy could join Trump's administration as secretary of the Department of Health and Human Services.

"I think that Bobby in a role like that would be excellent," Shanahan said. "I fully support it. I have high hopes."

Shanahan also referred to "risk of a Kamala Harris and [Tim] Walz presidency," without elaborating.

Kennedy, 70, was an environmentalist and lawyer earlier in life.