Aides and supporters of Barack Obama and Hillary Clinton are searching for an alternative to Rep. Keith Ellison, the early favorite in the race to head the Democratic National Committee, amid growing resistance to his bid.

The liberal Minnesota congressman has faced vocal criticism from prominent Democrats, Jewish groups and some union leaders, who have questioned his comments about Israel, his defense of Nation of Islam leader Louis Farrakhan and his commitment to the Democratic Party.

Hoping to assuage some of the concerns, Ellison said Wednesday that he'll resign his seat in Congress if he's picked as chairman by DNC members at the late February elections.

"Whoever wins the DNC chair race faces a lot of work, travel, planning and resource raising," Ellison said in a statement. "I will be 'all in' to meet the challenge."

But that promise may not be enough to save his bid.

The race to replace chairwoman Debbie Wasserman Schultz is taking shape as a proxy war for the future of the party, with backers of Vermont Sen. Bernie Sanders throwing their support behind Ellison as some supporters of Hillary Clinton search for an alternative.

The contest has divided top Democratic leaders, placing Obama's team at odds with Senate Democratic leader Harry Reid and his replacement, Chuck Schumer, whose early support for Ellison was seen as an effort to shore up the liberal flank in Congress.

Part of the issue is personal: Ellison has, at times, broken ranks to criticize Obama, the head of the party he now hopes to lead.

"Keith deserves the level of respect and deference he gave to Barack Obama for the last four years," said David Brock, a prominent Democratic activist and longtime Clinton ally.

While White House aides say that Obama is unlikely to publicly comment on the race, behind the scenes his backers have been speaking with top Democratic donors and potential candidates to see who else might be persuaded to run, said several Democrats familiar with the discussions.

High on the White House's list of preferred candidates is former Labor Secretary Tom Perez, who's weighing whether to run for DNC chair or for Maryland governor, said the Democrats, who requested anonymity to discuss private conversations. A vocal contingent is pushing for a Latino leader, arguing that the growing demographic group is crucial to the party's future and should be represented at the highest levels of its leadership.

Others, including former DNC Chair Ed Rendell, have been trying to draft Vice President Joe Biden, who's ruled out a bid. Biden spokeswoman Kate Bedingfield said he's "not interested" in the job but plans to stay heavily involved in shaping the party's future.

Former Michigan Gov. Jennifer Granholm, who would have been a prime contender for the post had Clinton won and has been quietly floated by some in the White House, has also told people she wouldn't take the job.

South Carolina party Chairman Jaime Harrison and New Hampshire party Chairman Ray Buckley have already announced bids, though they haven't gotten much traction within the party.

And Missouri's Secretary of State Jason Kander, who attracted attention for running a surprisingly competitive Senate race this year, says he's gotten calls exploring his interest in the post.

"I'm going to do all that I can for the cause of progress," Kander said. "If it turns out that my party wants me to serve as chair I'm open to that."

Ellison backers argue that the party must take a more populist approach after the 2016 losses, saying Democratic leaders did too little to address the economic pain of working class voters.

"Keith brings a breath of fresh air to the Democratic party," said DNC member Lee Saunders, president of the American Federation of State, County and Municipal Employees. "He believes in strengthening the economics for working families across the country."

But some party hands are more concerned with campaign mechanics than message, saying the party's outreach, bench and fundraising languished under Wasserman Schultz.

"Ellison talks about vision when we need a fundraiser and organizer," said Bob Mulholland, a longtime California Democratic operative and DNC member.