Acting Attorney General Matt Whitaker has been engaged in “robust” preparations for his Feb. 8 appearance before the House Judiciary Committee for weeks, including several mock hearings and briefings from all components within the Justice Department, according to senior DOJ officials.

Meanwhile, the committee's chairman, Jerry Nadler, D-N.Y., has said he plans to draft a subpoena out of an abundance of caution, in case Whitaker won’t answer the committee’s questions. Senior DOJ officials told Fox News the department had a “fulsome letter in response [to Nadler] addressing executive privilege.” DOJ officials said Nadler will receive the response letter prior to Friday’s hearing.

Senior DOJ officials also told Fox News they will be monitoring the committee’s markup hearing on Thursday, where the subject of a potential Whitaker subpoena may emerge again, adding that the acting attorney general has volunteered, and is eager, to appear at Friday’s hearing.

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DOJ sources call the idea of a subpoena of the acting attorney general “unprecedented,” adding that the department’s Office of Legislative Affairs has never seen anything like it.

“When did we start subpoenaing witnesses who come in voluntarily? The majority had enough faith in its witnesses last week not to subpoena them,” said Ranking Member Doug Collins, R-Ga. “The key difference today is simply that this witness is part of the Trump administration—and now we’re setting a dangerous precedent. The message to witnesses here is, if you make the time and effort to appear of your own accord, Democrats are going to subpoena you anyway.”

Whitaker was appointed as acting attorney general after President Trump fired Jeff Sessions following the 2018 midterm elections. Trump was seen as losing confidence in Sessions after the attorney general recused himself from Mueller’s investigation into Russian meddling in the 2016 presidential election.

Whitaker’s testimony comes just a week after he told reporters in an unorthodox move that Mueller’s probe was “close to being completed.”

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House Intelligence Committee Chairman Adam Schiff, D-Calif., called Whitaker’s comments inappropriate.

Whitaker also may be questioned about payments he received from a nonprofit foundation before he was appointed acting attorney general. Documents showed that he received nearly $1 million from the Foundation for Accountability & Civic Trust from 2016 to 2017.

The Associated Press contributed to this report.