STORY: A growing number of Republicans in Congress voiced concern on Monday over the Trump administration's threat to indict Federal Reserve Chair Jerome Powell.

Senator Thom Tillis was the first to announce plans to resist the Justice Department's criminal investigation into Powell.

Columbia Law School professor Kathryn Judge explains.

JUDGE: "Senator Thom Tillis, a Republican who is on the [Senate] Banking Committee, has expressed significant concerns about this development and has vowed not to move forward with the nomination hearings for Powell's successor chair until this matter is resolved. So part of what we're seeing here is this might actually trigger backlash that really undermines President Trump's ability to pursue his agenda as he had hoped."

The DOJ's investigation concerns allegations that Powell misled Congress in testimony related to a renovation of the Fed's headquarters complex in Washington.

Republican Senator Kevin Cramer criticized cost overruns on that project but said, "I do not believe, however, he is a criminal." He also said he hoped the investigation would end quickly, adding, "We need to restore confidence in the Fed."

JUDGE: "Nobody thinks that Chair Powell willfully misled Congress as would be required for that criminal indictment to really come through and come to fruition. The real concern here is that you're using levers that are meant to be used solely for purposes of true criminal activity and instead being used for political ends."

Powell called the administration's move a "pretext" to influence interest rates after a long-running pressure campaign to dramatically lower them.

The DOJ's move sent rates on longer-term U.S. Treasury bonds higher, as investors parsed what a less independent Fed could mean for inflation and monetary policy.

Former Fed chairs Janet Yellen, Ben Bernanke and Alan Greenspan joined with former federal government economic policy leaders from both political parties in raising the alarm over a less independent Fed.

But on Monday, White House Press Secretary Karoline Leavitt denied Trump's direct involvement:

REPORTER: "Did the president ever direct DOJ officials to open an investigation into Powell?"

LEAVITT: "No." (flash)

LEAVITT: "Well, look, the president has every right to criticize the Fed chair. He has a First Amendment right just like all of you do. And one thing is for sure, the president's made it quite clear, is Jerome Powell is bad at his job. As for whether or not Jerome Powell is a criminal, that's an answer the Department of Justice is going to have to find out."

A Justice Department spokesperson declined to comment on the case but added: "The Attorney General has instructed her U.S. Attorneys to prioritize investigating any abuse of taxpayer dollars."