A court fight could be brewing over President Donald Trump's move to name an interim head of a consumer protection agency despite the departing director appointing a deputy to temporarily fill that spot.

Both the Trump administration and the agency's departing chief, Richard Cordray, contend that the law is on their side and that their pick is the rightful leader.

Trump's choice as head of the Consumer Financial Protection Bureau is his budget chief, Mick Mulvaney, a former congressman who's called the agency a “joke,” an example of bureaucracy run amok. He is expected to dismantle much of what the bureau has done.

Cordray, an Obama appointee long criticized by congressional Republicans as overzealous, submitted his resignation Friday and elevated chief of staff Leandra English into the deputy director position.

A Senate GOP leader pledged swift action whenever Trump nominates a permanent head of the agency but believes the dispute with Democrats over the temporary appointment “ends up in court.”

Beyond the fight over who's calling the shots come Monday is the future direction of the bureau, created after the 2008 financial crisis and given a broad mandate as a watchdog for consumers when they deal with banks and credit card, student loan and mortgage companies, as well as debt collectors and payday lenders.

“All Americans should be deeply concerned about the White House's cynical decision to flout the law and attempt to put the ringleader of its dangerous, anti-consumer protection policies in charge,” House Democratic leader Nancy Pelosi of California said in a statement.

Taking aim at Mulvaney, she said the public deserves “a champion that protects them from predatory bankers and lenders, not the leadership of a Wall Street pawn who denigrates consumer protection as a 'sick, sad joke.”'

Democrats, she said, “will be firm in defending the rightful appointment” of English.

Sen. John Thune of South Dakota, the third-ranking GOP leader, said he expected that Mulvaney “will be on the job and he'll be calling the shots over there” on Monday. But, he added, “ultimately, this may end up in court.”

With Mulvaney there “for the foreseeable future,” Thune said on “Fox News Sunday,” he hopes eventually to see “reforms to that agency, which has essentially very little accountability to the Congress or anybody else.”

In installing Mulvaney, the White House has cited the Federal Vacancies Reform Act of 1998. Administration officials acknowledge that some other laws appear to clash with the Vacancies Act but said that in this case, the president's authority takes precedence.

In tapping English, Cordray relied on the Dodd-Frank Act, which created the agency, for the chain of succession.

That law says that “when the director steps aside, the deputy director shall be in charge of the agency — not may, shall be in charge,” said Illinois Sen. Dick Durbin, the No. 2 Democrat.

He said on CNN's “State of the Union” that “Wall Street hates it like the devil hates holy water. And they're trying to put an end to it with ... Mulvaney stepping into Cordray's spot. But the statute is specific, it's clear, and it says that the deputy shall take over.”

But Sen. Lindsey Graham, R-S.C., said he thinks Trump was on “good ground” to pick Mulvaney for the job and hopes Mulvaney “will ride herd on these folks.”

It's unclear when Trump might nominate a permanent director, who is subject to Senate confirmation.

“The best thing Congress can do is the president make a permanent nomination and we'll process it as quickly as we can in the Senate and get somebody installed as soon as possible. That ultimately is the best way to resolve this,” Thune said. “In the meantime, the president has made this appointment.”