Sen. Bernie Sanders of Vermont went to bat Wednesday for Rep. Keith Ellison’s bid to become the next chairman of the Democratic National Committee, saying the status quo is not working and that the Minnesota Democrat has the gumption to move the party in a different direction.

Speaking at an event hosted by the American Federation of Teachers in Washington, Mr. Sanders said the Democratic Party must change course after losing so much ground in Congress and in statehouses across the country over the past decade.

“Brothers and sisters, the status quo is not working and we will not succeed if we continue along the same-old/same-old path,” Mr. Sanders said at a campaign event with Mr. Ellison. “Now is the time for real change in the Democratic Party.”

“Now is a time for a chair of the Democratic Party who has a very different vision of the party than those that are in control today,” said Mr. Sanders, a self-described socialist. “Now is the time for Keith Ellison to become chair of the Democratic Party.”

Mr. Ellison, the co-chairman of the Congressional Progressive Caucus, has emerged as the front-runner in his race against South Carolina Democratic Chairman Jaime Harrison and New Hampshire Democratic Chairman Raymond Buckley.

But the race could be shaken up Thursday if, as expected, Secretary of Labor Tom Perez enters into the race amid speculation that President Obama and Vice President Joseph R. Biden urged him to get in the race.

“It’s certainly true that President Obama thinks very highly of the Secretary Perez,” White House Press Secretary Josh Earnest told reporters Wednesday. “He is somebody who has served at the Department of Labor for three or four years now, and he has been instrumental in advancing some executive actions of President Obama has prioritized.”

“But as I’ve said before,” he added. “I don’t anticipate a situation in which the president forcefully endorses a candidate in the DNC chair’s race.”

For his part, Mr. Ellison vowed Wednesday to “reset” the party by making sure that it is a bottom-up, rather than top-down organization, and by standing up for Democratic principles that he said will likely come under assault.

“I don’t know what stage in the whole spectrum of grief you may be at, but I think we need to arrive at acceptance that he is about to be the president,” Mr. Ellison said of Mr. Trump. “That means that each of us and all of us has to do everything thing we can to protect our fellow Americans, and to advance the cause of economic and social justice.”

“This is a history moment, this is a movement moment, and this moment may well be the moment when the American people fought back to reclaim their democracy — of, by, and for the people,” he said, arguing it is time to reset the future of the party.

“We have to reset the Democratic Party on the basis of grassroots activism. We have to reset the Democratic Party on the basis of working people that are striving every single day to make a better life for themselves and their families,” said Mr. Ellison, who has been raking in the endorsements.

New York City Mayor Bill De Blasio jumped aboard his campaign Wednesday, following in the footsteps of the AFL-CIO and Sens. Chuck Schumer of New York and Elizabeth Warren of Massachusetts.

But he also has faced a barrage of questions over writings from the 1990s in which he defended Louis Farrakhan against charges he was a racist and an anti-Semite, and called for a separate black state in America.

During an appearance Wednesday on “Morning Joe,” Mr. Ellison said the attempts to use his past comments against him are the product of “bad reporting” and a “smear campaign.”

“This is about distracting and taking people away from the issues that really are at hand in this case,” he said. “I think it serves somebody’s political purpose to push this stuff, but it doesn’t serve the public interest to serve it.”