Former Vermont Gov. Howard Dean (D) endorsed Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE for president on Wednesday, giving her the support of a liberal firebrand at a time when others on the left remain skeptical.

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"Hillary Clinton is by far the most qualified person in the United States to serve as President," Dean wrote in an op-ed in Politico Magazine. "If she runs, I will support her."

Dean, who caught fire among the liberal base in the 2004 presidential campaign before ultimately losing the nomination to John Kerry John Forbes KerryThe Memo: Warning signs flash for Trump on debates Divided country, divided church TV ads favored Biden 2-1 in past month MORE, offers Clinton support, while liberal groups are organizing to urge Sen. Elizabeth Warren Elizabeth WarrenGOP set to release controversial Biden report Biden's fiscal program: What is the likely market impact? Warren, Schumer introduce plan for next president to cancel ,000 in student debt MORE (D-Mass.) to challenge her from the left.

Those liberal groups include Democracy for America (DFA), which was founded by Dean himself. On Tuesday, DFA announced that it was asking its members to vote to join the "Draft Warren" movement begun by another liberal group, MoveOn.org.

"Washington consultants can spout off a dozen reasons why Elizabeth Warren shouldn't run, but none of that beltway blather means a thing next to this one, simple truth: The Democratic Party and our country desperately need Warren's voice in the 2016 presidential debate," DFA Executive Director Charles Chamberlain said in a statement announcing the Draft Warren move.

Neil Sroka, a spokesman for DFA, wrote on Twitter that Dean's op-ed was placed last week, before DFA's decision to join the Draft Warren effort. In a statement, Sroka said that if Clinton wins the nomination, "DFA members will work non-stop to help her make history," but, frankly, they'd prefer the senator from Massachusetts.

"The strong support for Warren and the bold populist progressive vision she's outlined for our country is why, later today, we'll ask our members to ratify our decision to join the emerging Draft Warren effort," Sroka said.

In supporting Clinton, Dean cited Supreme Court appointments, the need for experience on national security matters and income inequality.

"Hillary Clinton will not shrink from this challenge," he writes. "In the coming months, I expect her to lay out her plans to attack income inequality and help rebuild the middle class. She knows how to sell a broad range of Americans on these policies, and has shown how to stand up against extremist economic policies."

Income inequality is the main issue spurring liberal groups to look for an alternative to Clinton. Dean acknowledges: "I am sure I will have disagreements with her as she focuses on getting Americans back to work and rebuilding an America that works for all of us."

However, he writes, "We need a mature, seasoned, thoughtful leader at a time when maturity and thoughtfulness are increasingly rare commodities in Washington, D.C."

Dean said in August that he is a "huge Hillary Clinton fan."

That was a shift from June 2013, when he told CNN that he was considering a run of his own, and said of Clinton, "She is not going to have a pass," Dean said. "There will be other people who will run."

Neither woman has announced a bid, and Warren has repeatedly said she is not running, which Dean, in an email to The Hill, said is reason enough to look elsewhere.

"I have no problem [with] DFA's efforts. We talked about this extensively. I take Elizabeth Warrens statements about not running at face value, and if she does run she will be a valuable voice for a lot of issues I care deeply about," Dean wrote.

— Updated at 11:35 a.m.