No Labels urges for a bipartisan ‘unity ticket.’ Democrats disagree.

More than 15,000 people in Arizona have registered to join a new political party floating a possible bipartisan “unity ticket” against Joe Biden and Donald Trump.

While that’s less than the population of each of the state’s 40 largest cities, it’s still a number big enough to tip the presidential election in a critical swing state. And that is alarming people trying to stop Mr. Trump from winning the White House again.

The very existence of the No Labels group is fanning Democratic anxiety about Mr. Trump’s chances against an incumbent president facing questions about his age and record. While it hasn’t committed to running candidates for president and vice president, No Labels has already secured ballot access in Arizona and 10 other states. Its organizers say they are on track to reach 20 states by the end of this year and all 50 states by Election Day.

“If they have someone on the ballot who is designed to bring the country together, that clearly draws votes away from Joe Biden and does not draw votes away from Donald Trump,” said Rodd McLeod, a Democratic strategist in Arizona.

That’s raising the stakes for Biden allies who are mounting a furious pressure campaign against No Labels and politicians taking meetings with the group.

In Arizona, which Mr. Biden won by about 10,000 votes, the state Democratic Party sued Secretary of State Adrian Fontes, also a Democrat, to try to prevent No Labels from being on the ballot. The party lost in court and then dropped its lawsuit. Now Democrats are pushing Mr. Fontes to force No Labels to disclose its donors, having insinuated that the group is being supported by conservatives attempting to thwart Mr. Biden. No Labels has so far refused to name how it is funding its work, saying it follows federal law and wants to protect the privacy of its donors.

Mr. Fontes has not commented publicly but is expected to announce a decision in the coming weeks after telling No Labels he may take action against the group for failing to register under the state’s campaign finance law. His decision is likely to be challenged in court.

Some of the anti-No Labels efforts here are quixotic. A perennial candidate from outside Phoenix signed up as a No Labels candidate and declared himself chairman of No Labels’ Pinal County chapter, in part so he could run for state office and try to force the party to follow the state’s campaign finance reporting laws.

“It’s kind of like a performance art piece,” said Richard Grayson, who promptly after switching to No Labels endorsed Mr. Biden and Vice President Kamala Harris.

Mr. Biden’s narrow 2020 victory came with the help of anti-Trump Republicans, right-leaning independents and voters who disliked both candidates but saw Mr. Biden as a better option than Mr. Trump. He’ll need their support to win a rematch.

In Arizona, Mr. Biden was endorsed by former Republican Sen. Jeff Flake and Cindy McCain, the widow of Sen. John McCain – a lifelong Republican who publicly clashed with Mr. Trump.

If even a small number of those voters were to back a No Labels candidate next year, Mr. Biden could fall short.

No third-party candidate has ever won the presidency or even come close. In the modern era, the strongest performer was Ross Perot in 1992, but he didn’t earn a single electoral vote. He did, however, earn a reputation as a spoiler to then-President George H.W. Bush.

Democrats blame Green Party nominee Jill Stein for spoiling Hillary Clinton’s would-be victory in 2016, when Ms. Stein got more votes in Michigan, Pennsylvania, and Wisconsin than Mr. Trump’s margin of victory. In 2020, a shift of just 45,000 votes in Arizona, Georgia, and Wisconsin would have been enough to tilt the election from Mr. Biden to Mr. Trump.

“We need to convince the political world that being involved with this is a bad idea,” said Matt Bennett, executive vice president of the center-left group Third Way. “If you’re a potential candidate of theirs, you’re going to be Jill Stein 2.0.”

But supporters of No Labels insist that the political climate is far different heading into 2024, with wide swaths of voters in both parties exhausted by years of turmoil and chaos in Washington.

“These are unprecedented times,” said Benjamin Chavis, a former head of the NAACP who is now working with No Labels. “Never before has such a large number of Americans expressed their concerns and expressed their views and their aspirations for more choices.”

At least 13,500 people have registered with No Labels in Arizona’s two largest counties, which include Phoenix and Tucson, with roughly 1,900 registered in the state’s other counties, according to the most recent figures available.

About half of registrants in August were formerly independent and another quarter were newly registered, according to Sam Almy, a Democratic data analyst based in Phoenix. The rest came mostly from the two major parties: 14% were previously Democrats and 11% had been Republicans.

While only about a quarter of the newly registered No Labels members came from the major parties, they’re much likelier to vote. About 63% of the former Democrats and 65% of the former Republicans voted in 2020, while only 45% of the former independents cast a ballot.

No Labels party members skew younger. More than half are younger than 35, according to Mr. Almy, and just 5% are older than 65. Twelve percent of them live in the 4th Congressional District, which includes Arizona State University.

If No Labels runs candidates, anybody can vote for them whether they’ve joined the party or not.

No Labels leaders say they’ll decide after the Super Tuesday primaries in March whether to run a candidate, who would be nominated at a convention in Dallas in April.

The group has not said how the candidate would be chosen but hopes to publish a plan next month. No Labels has ties to moderates from both parties. Among them: Democratic Sen. Joe Manchin of West Virginia, former independent Sen. Joe Lieberman of Connecticut, former Republican Gov. Jon Huntsman of Utah, and Republican Gov. Larry Hogan of Maryland. The group also could pick a business leader or retired military officer.

Ryan Clancy, chief strategist for No Labels, said their decision will not be influenced by head-to-head polling of the chosen candidate against Mr. Trump and Mr. Biden. Such a poll would be meaningless because a large swath of voters won’t know anything about the No Labels candidate before a campaign is run, he said.

No Labels leaders vehemently deny that they’ll be a spoiler for Mr. Trump and say they’ll only proceed if their candidate has a path to victory. But it’s unclear how certain that path will have to be.

“This is something we’re still working through,” Mr. Clancy said.

This story was reported by The Associated Press.