Labor Secretary Tom Perez will launch a campaign to be Democratic National Committee chairman this week, becoming the first serious challenger to Rep. Keith Ellison (D-Minn.) for a lead role in rebuilding a shellshocked party.

According to two sources familiar with Perez’s thinking, he will announce his candidacy Thursday, a day after a planned rally for Ellison with the American Federation of Teachers and Sen. Bernie Sanders (I-Vt.).

The announcement would come after weeks of quiet pressure on Perez to give Democrats another alternative to the Minneapolis congressman. The New York Times first reported his plans.

A spokesman for Ellison said there would be no comment until Perez made his bid official, but the two other candidates for the job welcomed him to the race.

“Tom’s a good friend, a great Democrat, and I welcome him to the race,” said Jaime Harrison, the chairman of the South Carolina Democratic Party. “I’m a firm believer that iron sharpens iron.”

Rep. Keith Ellison (D-Minn.) served two terms in Minnesota’s legislature and has served five terms in Congress. (Saul Loeb/AFP/Getty Images)

“I spoke with Secretary Perez today [and] welcomed him to the discussion about the future of the Democratic Party,” said Ray Buckley, chairman of the New Hampshire Democratic Party. “I am confident by the time the DNC meets in 10 weeks, the party will have had ample opportunity to hear our plans and participate in an open and vibrant process.”

Each candidate comes from the progressive wing of the party; there is no discussion, as there was after the party’s 1988 or 2004 defeats, of tacking right.

Pete Buttigieg, the 34-year-old mayor of South Bend, Ind., who has already earned a shoutout from President Obama, also is considering a run, according to Democrats familiar with his plans.

Buttigieg, whom some Democrats had hoped would consider higher office in Indiana, is said to have concluded that a DNC post would be a better use of his talents, according to people who have spoken with him.

He earned national attention for his innovative work in the industrial city and also because he is gay. A New York Times op-ed in the summer touted him as potentially the nation's first gay president

Meanwhile, there’s less drama in the race to lead the Republican National Committee, where president-elect Donald Trump is expected to endorse either Georgia strategist Nick Ayers or Michigan GOP chair Ronna Romney-McDaniel as a successor to incoming White House chief of staff Reince Priebus.

Ellison, the first Muslim elected to Congress, was the first candidate in the DNC race, with backing from Sanders and incoming Senate Minority Leader Charles E. Schumer (D-N.Y.).

“When the DNC opened up, [Sanders] called me and said we need to make the DNC not a fundraising and political organization but a true organizing tool,” Schumer told The Washington Post earlier this month. “I said, ‘You’re exactly right.’ And he says, ‘The guy to do it is Keith Ellison.’ ”

Since then, Ellison has fended off fresh stories about his support for the Nation of Islam when he was younger and his criticism of Israel’s treatment of Palestinian citizens. The stories were not surprising, echoing the attacks that have come Ellison’s way whenever his profile had risen.

Privately, Democrats say Ellison has locked up the support of perhaps one-eighth of the 450-odd voting DNC members. The Anti-Defamation League, which initially praised Ellison, admitted “serious doubts” about him after conservative media publicized a 2010 speech in which the congressman suggested “a country of 7 million people” had too much weight in America’s approach to the Middle East.

“He is clearly an anti-Semite and anti-Israel individual,” Haim Saban, an Israeli-American businessman and a Democratic Party donor, said at a December policy forum endowed by his donations. “Keith Ellison would be a disaster for the relationship between the Jewish community and the Democratic Party.”

Ellison has apologized for some of his old remarks, writing in a Washington Post op-ed this month that he “rejected all forms of racism and anti-Semitism” but “should have listened more and talked less.” In interviews Wednesday, neither Ellison’s rivals nor the state party chairs who will vote on the next chairman criticized his old remarks. The bigger stumbling block had been that Ellison serves in Congress — a problem he had ameliorated, at a DNC gathering last week, by saying he would quit that job if elected.

Perez’s decision is seen as an effort by the exiting Obama-era leadership to keep control of the party in trusted hands. For Sanders supporters, for whom Hillary Clinton’s loss provided bitter vindication, that’s a strike against Perez. From inside the Obama administration, Perez had supported the Trans-Pacific Partnership, a non-starter for many progressives.

“A Perez candidacy will undoubtedly create another Clinton-vs.-Sanders debate and divide the party,” said Jane Fleming Kleeb, a climate change activist and Ellison backer who chairs the Nebraska Democrats. “Tom Perez is another suit, and we don’t need another suit running the party. We need someone from middle America who knows how to organize and respects the grass roots.”

Perez, who has not commented on the DNC run, has less of an electoral record to present. The Detroit-born Ellison served two terms in Minnesota’s legislature and five terms in Congress, and he cites that as proof he can turn out the electorate that will bring Democrats back across the country. Perez never won an office higher than county council in Maryland. In the summer, Progressive Change Campaign Committee founder Adam Green said that Perez would be a fine choice for vice president; today, he argued that Ellison clearly outclassed the labor secretary when it came to leading the DNC.

“Hopefully [Perez] will be attorney general someday,” Green said in a statement. “His mind is needed on important policy issues, and he could be a leader right now helping Silicon Valley companies figure out a gig economy that works for workers. He has a different set of superpowers than those needed to be the DNC Chair.”

Perez’s relatively late decision also came after major labor unions, including the AFL-CIO and AFT, had gotten behind Ellison. “We love Tom Perez,” said AFT president Randi Weingarten. “We have worked with Tom, and he’s done a great job as secretary of labor, but Keith is an organizer who can unite and rebuild the party from the grass roots up.”

For Ellison’s backers in the states, the choice was simple: They knew Ellison, and he knew them. Martha Laning, the chairman of Wisconsin’s Democrats, credited Ellison with coming to the state for low-profile visits that revved up activists.

“He didn’t just come in and give a speech and leave,” said Laning. “He really talked to the people. We just had an election where rural areas that had voted Democratic in the past voted for Donald Trump, so we need to rebuild from the grass roots up.”

Kleeb gave Ellison similar praise for a speech at the party’s annual fundraising dinner. If elected, she said, he could be counted on to help Democrats in places they’d seemingly cut loose — and to follow activists where they were leading.

“I haven’t seen Tom Perez at the front of marches in the last 10 years,” said Kleeb. “He could have used his position as secretary to bring together labor and environmentalists to talk about jobs. We were crying out for that type of leadership, and he failed.”

Ed O’Keefe and John Wagner contributed to this report.