Newly empowered congressional Democrats are gearing up for their first battle with the Trump administration over the acting attorney general appointed after the president fired Jeff Sessions, demanding he follow Sessions’s example and recuse himself from overseeing the special counsel’s Russia investigation.

Congressman Jerry Nadler of New York, the likely incoming chairman of the House Judiciary Committee, called the acting attorney general, Matthew Whitaker, “a complete political lackey.” Speaking Sunday on CNN’s State of the Union, Nadler said Whitaker will be “our very first witness” summoned, or subpoenaed if necessary, once the Democrats assume control of the House of Representatives in January. Nadler said he will ask how Whitaker can be trusted to impartially supervise an investigation that he publicly criticized as a cable-news commentator.

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“He’s already prejudged the Mueller situation,” Senator Chuck Schumer of New York, the Democratic minority leader in the Senate, said on the same program. “If he stays there, he will create a constitutional crisis by inhibiting Mueller or firing Mueller.”

Schumer added that he and House Democratic Leader Nancy Pelosi have sent a letter to the Justice Department’s chief ethics official asking whether Whitaker should recuse himself from overseeing the Russia probe, as Sessions did, drawing Trump’s ire early in his administration. The letter reportedly asks Assistant Attorney General Lee Lofthus, a career official, whether he has already issued guidance on a possible recusal, which would not automatically become mandatory.