(Bloomberg) -- President Joe Biden expressed concern over an effort by the group No Labels to consider mounting a third-party 2024 presidential ticket, saying it would only serve to help elect the Republican nominee.

Biden in an interview with ProPublica published Sunday was asked about the involvement of his onetime colleague, former Senator Joe Lieberman of Connecticut, in the effort to organize a potential third-party challenge.

“Well, he has a democratic right to do — there’s no reason not to do that. Now, it’s going to help the other guy and he knows,” Biden said. “That’s a political decision he’s making that I obviously think is a mistake. But he has a right to do that.”

Biden’s comments underscore growing concern in Democratic circles that No Labels, a centrist advocacy group, will field its own candidate as an alternative to the nominees on the major-party tickets. Polls show voter unease about a potential rematch between Biden, who does not face a serious primary challenger, and former President Donald Trump, the clear frontrunner for the GOP nomination. 

Earlier: Half of Voters Open to Third Party, Worrisome Sign For Biden

West Virginia Senator Joe Manchin, a conservative Democrat, has refused to rule out a third-party bid and appeared at a No Labels in New Hampshire in July. 

Asked about the speculation over a 2024 bid, Manchin told Fox News Sunday he would make a decision by the end of the year and that candidates needed to reject the extremes in their parties.

“This country does not run on the fringes,” he said. “It never has. And it can’t start now. So they’re either going to come back or we’re going to bring it back.” 

Also on Sunday, Representative Dean Phillips of Minnesota announced he was leaving his House Democratic leadership post because of “incongruent convictions” related to the 2024 presidential race.

While he didn’t elaborate, Phillips was among the first Democrats to publicly say Biden should step aside and allow more “dynamic” Democrats to seek the party’s nomination. He later suggested that he was considering a White House run himself.

More recently, he has hinted that he would consider supporting a third-party choice. Phillips, who has been co-chair of the Democratic Policy and Communications Caucus, has drawn criticism from some Democrats who say his comments about Biden’s age give Republicans political ammunition.

Responding to Biden’s interview, Lieberman said in a No Labels statement that if the group “concludes that a bipartisan Unity ticket has no chance to win and may only be a spoiler, we will stand down and not offer our ballot line to a third ticket.”

Biden said the Democratic party needed to do a better job speaking to the concerns of blue-collar voters, whose support will be crucial to his reelection hopes.

“The fact is we’re going to be very shortly a minority White European country. And sometimes my colleagues don’t speak enough to make it clear that that’s not going to change how we operate,” Biden said.

Biden and Trump made dueling visits to the Michigan last week in a bid to court members of the United Auto Workers union who are striking against Detroit’s Big Three Legacy automakers, highlighting how the battle for blue collar workers has become a campaign flashpoint. Biden made an historic visit to a picket line while Trump spoke at a nonunion supplier of parts.

Earlier: Biden Hits at Trump Over EV Criticism in Fight for Union Support

“A lot of the guys I grew up with in Claymont, Delaware, and Scranton, Pennsylvania, they feel like they’re not being respected. Not so much by policy just by the, by the failure to talk about their needs,” Biden told ProPublica. “I’ve talked about building a country from the middle on the bottom up, not the top down, and that includes everybody, and embracing — embracing the blue collar workers.”

--With assistance from Ian Fisher, Billy House and Gregory Korte.

(Updates with Phillips leaving Democratic leadership in eighth paragraph, No Labels response in 11th.)

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