Rep. Sander M. Levin of Michigan is stepping aside as ranking member on Ways and Means, opening the door to a competition for the tax-writing panel’s top Democratic slot.

Levin, 85, cited two reasons for not seeking re-election to the Ways and Means ranking position in a letter to colleagues.

“First, it is imperative that we support younger members as they seek to fully assume the mantle of leadership in the four years ahead, as we also continue to tap the experience of those who have led so many of these battles,” Levin said, in reference to Democrats holding President-elect Donald Trump’s administration accountable. He called Trump’s election “an ‘all hands on deck moment.’ ”

“Second, I want to be free to focus in addition to tax reform on two of my legislative passions: health care and trade,” he added.

Levin’s announcement has sparked a fight over his successor as ranking member on Ways and Means, the oldest committee in Congress and one of the most influential with its jurisdiction over taxes, health care, trade and entitlement programs such as Social Security.

Reps. Richard E. Neal of Massachusetts and Xavier Becerra of California signaled Tuesday that they will seek the ranking member position. Neal, 67, has a long record of developing bipartisan tax ideas and legislation. Becerra is the outgoing chairman of the House Democratic Caucus.

Becerra, 58, immediately won the support of Levin, who said he planned to promote the Californian.

“I’m backing Xavier,” Levin said simply.

Rep. John Lewis, D-Ga., is the most senior Democrat on the committee after Levin who will be returning in the 115th Congress. He declined to comment on whether he would join Neal and Becerra in the race for ranking member.

Fundraising for colleagues often plays a role in committee leadership fights. According to the Center for Responsive Politics, Neal’s leadership political action committee raised $382,000 and closed with cash on hand of $847,000 in the 2016 cycle, and Becerra’s leadership PAC raised $564,000 and closed with $94,000 in the same period.

Levin circulated his letter on the eve of Democratic leadership elections. His longtime ally, Minority Leader Nancy Pelosi, D-Calif., faces a challenge from Rep. Tim Ryan, D-Ohio.

“Our caucus is deeply grateful for Sandy Levin’s leadership on Ways and Means, and we will continue to be strengthened by his wisdom as Republicans begin their assault on Medicare and the health care of 20 million previously uninsured Americans,” Pelosi said in a written statement.

The Democratic leader has offered to restructure her leadership team to add more younger members in the next Congress. But she also has defended the seniority system that allows ranking members on committees to serve indefinite terms. The top Democrats on committees are not subject to term limits like those established by the GOP for committee chairmen.

A longtime ally of labor and the automobile industry, Levin took over as chairman of Ways and Means in March 2010, when Charles B. Rangel, D-N.Y., ceded the gavel while he was under an ethics investigation. Levin has served as ranking member since 2011.