More than three dozen lawmakers are already planning to leave Congress next year. But there’s another impending legislative branch retirement that could have major implications in Washington.

Comptroller General Gene Dodaro, who heads the Government Accountability Office, hits the end of his 15-year term Dec. 22 and will be forced to vacate the post that occupies an increasingly crucial — and politically charged — oversight role.

The comptroller general is uniquely empowered to call out the president for breaking the law by withholding federal cash, and Dodaro has done so repeatedly over the past eight months — putting himself at the center of a largely partisan fight over President Donald Trump’s funding moves that has exacerbated tensions between the White House and Capitol Hill.

Now Trump gets to nominate Dodaro’s replacement, and key lawmakers are only just starting to take stock of a paradox: A president who continually tests the bounds of Congress’ spending powers gets to pick the legislative branch’s chief watchdog.

“It sets up a very bad situation,” Sen. Brian Schatz of Hawaii, the next Senate Democratic whip and a senior appropriator, said in an interview. “Among the things to be alarmed about, this is a new one.”

The stakes are high: Whoever ends up running GAO once Dodaro’s term ends will be able to bolster, or undermine, Congress’ defenses against Trump in the separation-of-powers battle the president is stoking by terminating, freezing and reallocating hundreds of billions of dollars Congress previously approved.

“When one party controls the Senate, the House and the White House, there’s a tendency to rally around the president and to do what the president wants,” said David Walker, Dodaro’s predecessor and the only living former GAO director. “But somebody’s got to be able to be the independent referee, and to try to do what they think is in the interest of the institution, the Congress and the country. And that’s what the comptroller general is.”

All of this is taking place as Trump administration officials and some congressional Republicans have been trying to downsize and discredit the watchdog. That has included publicly questioning the GAO’s authority and accusing the agency of siding with Democrats in its multiple determinations that the White House unlawfully flouted Congress’ “power of the purse.”

White House budget director Russ Vought said this month that GAO is “a quasi-legislative independent entity … something that shouldn’t exist.”

There have been other slights, too. In the Senate, the GAO told Republicans they could not skirt the filibuster in voting to override California’s pollution standards; Republicans did so anyway. In the House, GOP lawmakers endorsed cutting the agency’s roughly $800 million budget in half for the upcoming fiscal year. And Elon Musk, prior to leaving the Trump administration, attempted to send in a Department of Government Efficiency team to assess the GAO for mass staff reductions.

Meanwhile, the legislative branch writ large has become more broadly vulnerable to the White House’s whims, seen most starkly in Trump’s abrupt firing of the librarian of Congress and the registrar of copyrights.

It’s not yet clear what the Dodaro succession plan will look like; a White House spokesperson did not respond to a request for comment.

A seven-member panel of lawmakers is supposed to recommend at least three replacement candidates for Trump to consider. By law, that group is composed of the top four leaders in each chamber, the chairs and ranking members of the key House and Senate oversight committees and the Senate president pro tempore.

However, most congressional leaders have yet to start hunting for qualified contenders, and furthermore seem largely unaware they have any role to play in filling the slot.

“I don’t even know the process,” Senate Majority Leader John Thune said in a brief interview. “It’s been a while. This hasn’t happened on my watch.”

Two of the would-be commission members had kind words for Dodaro, including Sen. Rand Paul, chair of the Senate Homeland and Governmental Affairs Committee.

“I’ve always appreciated him, and I think he’s a straight shooter,” the Kentucky Republican said in an interview.

Sen. Gary Peters (D-Mich.), the panel’s ranking member, said he “would want somebody like Gene, who has been a really solid member.”

On the House side, Oversight Chair James Comer (R-Ky.) said in an interview he’s looking for the next GAO director to be “an aggressive person that looks for waste, fraud and abuse.”

Comer added, “We want someone that communicates regularly with Congress, so we can kind of have an idea of what they’re doing.”

But Trump could instead ask Republican senators to confirm a new watchdog of his own choosing — or forgo making a nomination altogether.

It would leave a leadership vacuum at the top of the agency that not only monitors whether Congress’ spending directives are followed but is also empowered to examine the effectiveness of federal agencies on behalf of lawmakers.

Further raising the stakes in confirming a new director, lawsuits are pending around the country challenging Trump’s withholding of congressionally approved funding, and a federal appeals court ruled this summer that only the GAO director can sue the administration for violating the decades-old impoundment law — not the groups that were set to receive the funding.

Dodaro has so far chosen not to sue the Trump administration for withholding funding. But when he steps down, he’ll be able to pick an acting GAO director who also would have the power to file a lawsuit if they so choose.

Still, said Molly Reynolds, head of governance studies at the Brookings Institution, “if you get a comptroller general in place who is Trump-friendly, that is going to foreclose that option” of GAO suing the administration.

An acting director also wouldn’t be “in a position to make major transformational changes,” warned Walker, the former GAO director.

When Walker resigned in 2008, he appointed Dodaro acting director, a title that stuck for more than two years because Congress and the president weren’t quick to work through the nomination process. Before that, it also took two years to formally install Walker in the post in 1998.

Walker is now urging congressional leaders to recommend candidates who are willing to challenge executive branch officials regardless of who is president, as he did during his own tenure. A political independent who “leans Republican” and was confirmed by a GOP-led Senate, Walker sued the Republican vice president, Dick Cheney, for failure to provide GAO access to records.

He is also agitating for lawmakers to quickly start the search for potential replacements: “There’s no reason that they shouldn’t be planning now so that they can end up trying to make a timely decision.”