WASHINGTON — Top Democratic strategists, including current advisers to President Biden and former U.S. senators, met last week with former Republicans who oppose Donald Trump at the offices of a downtown Washington, D.C., think tank.

Their mission: to figure out how to best subvert a potential third-party presidential bid by the group No Labels, an effort they all agreed risked undermining Biden’s reelection campaign and reelecting former president Donald Trump to the White House.

President Biden speaks at the League of Conservation Voters annual capital dinner in Washington on Wednesday. Susan Walsh/Associated Press

The broad show of force at the off-the-record gathering – with about 40 people in the room and others appearing on Zoom on the anniversary of D-Day – was just the latest sign of growing concern in some political circles about the No Labels effort to get ballot access to challenge the major-party candidates next year.

Attendees included former White House chief of staff Ron Klain, Democratic National Committee senior adviser Cedric L. Richmond and Stephanie Cutter, a former campaign adviser to Barack Obama who has worked with the Biden team. They were joined by former senators Doug Jones, D-Ala., Heidi Heitkamp, D-N.D., and Claire McCaskill, D-Mo., along with representatives of the anti-Trump Lincoln Project, former Weekly Standard publisher Bill Kristol and Lucy Caldwell, a former Republican consultant who now advises the independent Forward Party, according to people present at the event, who spoke on the condition of anonymity because the event was private.

“I see a group, under a catchy slogan that is misleading at best, saying that they have the country’s best interest at heart when the exercise will do nothing but elect Donald Trump,” said Richmond, who like Klain and Caldwell told The Washington Post that they attended in their capacities. “I am encouraged that a lot of people share the concern that this effort is dangerous.”

No Labels, a nonprofit group that does not disclose its donors, has been working to qualify a new party of the same name for state ballots in 2024 that could be used by an independent bipartisan presidential ticket in case the major parties nominate “unacceptable” candidates. The group’s leaders have said they view Trump as unacceptable while telling others that they would not move forward if Florida Gov. Ron DeSantis wins the Republican nomination.

The group has declined to say definitively that it views Biden as unacceptable, though many Democratic strategists fear the effort will move forward if Biden and Trump are the nominees.

The Arizona Democratic Party has sued to kick No Labels off the ballot in that state, alleging that its application was deficient. Maine Secretary of State Shenna Bellows, a Democrat, recently sent letters to more than 6,000 people who had enrolled in the No Labels party in her state, notifying them of concerns that they may have been tricked into signing what they thought was a petition when in fact they were changing their party registration.

No Labels fired back at Bellows on Tuesday with a letter asking for the evidence that prompted her to target the voters individually who had signed documents. A No Labels attorney from Marcus Clegg, a firm based in Portland, alleged that Bellows’s actions potentially “had a chilling effect” on voters. In a clear suggestion of potential litigation, the letter cited Supreme Court precedent that says it is illegal to discriminate against “new or small political parties.”

Bellows responded to the letter in a statement to The Post on Tuesday.

“Ensuring that Maine voters have the information they need to exercise their First Amendment rights to associate with the party of their choice (or no party) is my main concern,” Bellows said. “The response we’ve seen from voters who received our letter has been overwhelmingly that of gratitude for the information provided.”

Benjamin Chavis Jr., a former executive director of the NAACP who now works with No Labels, said the people working to stop the group misunderstand its intentions and are undermining the electoral process. No Labels leaders have said they will decide in 2024 whether to move forward with a presidential campaign based on whether there is a clear path to victory with named candidates.

“I’ve spent my entire life in the Democratic Party, championing civil and voting rights and I’ve always believed our democracy is stronger when there are more voices and choices in our political process. That’s why I was so disturbed to hear that a group of my friends and leaders in the Democratic Party recently convened to try to undermine No Labels’ 2024 presidential insurance project,” Chavis said in a statement. “No Labels will not spoil this election for Trump. What we will do is continue working resolutely to give millions of Americans a choice they so clearly want.”

Matt Bennett, the executive vice president for Third Way, which hosted the event, declined to comment, citing the confidentiality of the proceedings. Klain is a former Third Way board member.

People who attended the June 6 meeting described presentations from recent polling and focus groups that suggested a No Labels campaign would draw more support from Biden than Trump in a hypothetical three-way matchup. They said attendees discussed efforts to put pressure on No Labels donors and to educate potential No Labels presidential candidates about the dangers of the effort resulting in Trump’s election.

They also spoke about raising more money to counter the effort and increasing outreach to members of Congress who are affiliated with the bipartisan Problem Solvers Caucus, which was founded with the help of No Labels, attendees said.

Among those present or connected by Zoom was Obama 2012 campaign manager Jim Messina, former Howard Dean 2004 campaign manager Joe Trippi, Democratic strategist Antjuan Seawright, Investing in U.S. co-founder Dmitri Mehlhorn and Lincoln Project co-founder Reed Galen, who previously worked as a Republican strategist, according to people present. Hilltop Public Solutions partner Patrick Dillon, a former Obama White House deputy political director who is married to White House deputy chief of staff Jen O’Malley Dillon, also attended, the people said.

“I thought it was a pretty mixed group,” said one participant, who spoke on the condition of anonymity to describe the event. “It was not like some progressive, Democratic caucus meeting.”