WASHINGTON – The incoming chairman of the House Judiciary Committee reissued a threat to subpoena acting Attorney General Matthew Whitaker on Wednesday, a day before Democrats assume control of the House.

In an interview with USA TODAY, Rep. Jerrold Nadler, D-N.Y., said Whitaker hasn’t “gone back” on a commitment he made during a December phone call to testify in January, “but they’ve been impossible, setting dates.”

“We will, if we have to, subpoena him and we will ask him, basically, about protecting the Mueller investigation,” said Nadler, who previously talked of issuing a subpoena for Whitaker in November.

Democrats are focused on protecting the work of special counsel Robert Mueller, who is leading the Justice Department's investigation into a host of issues, including whether the Trump campaign cooperated with Russia to influence the 2016 election. They will have the power to subpoena witnesses in the House since winning control in the November midterm elections.

As they look ahead to numerous oversight investigations, Nadler said the first thing he’ll do is “call in” Whitaker, who has refused to recuse himself from overseeing the Mueller probe even though a Justice ethics official recommended he do so.

Whitaker's oversight had been seriously questioned because he was sharply critical of the Mueller probe before he joined the department in 2017 as chief of staff to then-Attorney General Jeff Sessions. Whitaker, who was named as DOJ's acting head after Sessions was fired in November, previously suggested that the probe should end and that the department could starve it of funding.

A Justice Department spokeswoman declined to comment.

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Nadler said Democrats on the committee will ask if he has “directed Mueller not to indict somebody” or not to pursue a particular line of inquiry.

“Has he communicated with the White House? Has he told the White House what the Mueller people are doing?” Nadler asked. “In other words, is he in any way improperly interfering with the investigation?”

Nadler said he will also ensure that a report on Mueller’s findings, once available, goes to Congress and the public – not just the attorney general.

“And we’ll use subpoena power, if we have to, for that,” he said.

President Donald Trump, who has railed against the Mueller probe as an unjustified "witch hunt," fired Sessions after the midterm election in November and named Whitaker acting attorney general. Trump has nominated William Barr as attorney general, and he awaits Senate confirmation.

Contributing: Kevin Johnson and Bart Jansen