The top Republican on the House Judiciary Committee is demanding to know why the panel's Democratic leadership made the "costly" and "unusual" decision this week to hire two prominent anti-Trump consultants to conduct a purportedly impartial investigation of the the White House.

In a letter to House Judiciary Committee chairman Jerry Nadler, D-N.Y., the ranking member on the committee, GOP Rep. Doug Collins, asked how much taxpayers could expect to be charged for Barry Berke and Norman Eisen's services -- as well as what exactly the pair of vocally anti-Trump operatives will be doing.

"Your unilateral decision to hire two individuals with such obvious bias against the president will taint anything they touch going forward," Collins wrote to Nadler. "Does the hiring of Mr. Berke and Mr. Eisen indicate a lack of confidence in your current staff to handle important matters regarding the president?"

In a recent report published by the Brookings Institution, Collins noted in the letter, Berke and Eisen wrote that publicly available evidence "strongly supports that the president obstructed justice under ordinary application of the relevant criminal law."

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And in a Washington Post op-ed last year, Berke and Eisen -- as well as co-author Noah Bookbinder -- wrote, "The president is aruging that not only is he above the law but also above the facts. That audacious move is unbecoming for our nation's chief law enforcement officer, and neither Mueller nor Congress should let him get away with it."

The three also wrote in The New York Times that "from the publicly available information, it's now clear that Trump obstructed justice."

Eisen served as a White House counsel for Obama and has focused on government ethics and corruption as a co-founder of the group Citizens for Responsibility and Ethics in Washington.

Berke, a litigation partner at the international law firm Kramer Levin, is based in New York City, and will commute four days per week to work for the Democrats on the Judiciary Committee. That arrangement, Collins asserted, constituted a problematic conflict of interest.

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"Is Mr. Berke assisting the Majority staff to drive more business to his law firm?" Collins wrote in the letter, which also queried Nadler as to who would be paying for Berke's hotel bills and other commuting costs.

"Is the nature of the Majority staff’s arrangement to pay Mr. Berke and Mr. Eisen by the hour?" the letter asked. "If so, what is the hourly rate? ... Did Mr. Berke and Mr. Eisen complete the appropriate paperwork authorizing outside income as House employees? If not, is the 'consultant' arrangement for Mr. Berke and Mr. Eisen simply a veil to enable the Majority to circumvent normal reporting procedures?"

Collins added: "The Majority staff is also allowing Mr. Eisen to retain his position at the Brookings Institution, an elite, liberal think-tank. Such arrangements are fraught with technical, legal, and financial conflicts of interest."

Eisen, Berker, and Nadler's office did not respond to Fox News' requests for comment. But in a statement Wednesday, Nadler called Eisen and Berke "two widely respected legal authorities" and said Democrats were determined to “ask critical questions, gather all the information, judiciously assess the evidence, and make sure that the facts are not hidden from the American people."

Nadler specified that Berke and Eisen have been retained on a consulting basis as “special oversight staff” and they would consult on matters related to the Justice Department and Special Counsel Robert Mueller’s investigation into Russian interference and connections to the Trump campaign.

Nadler's statement also included praise for Berke and Eisen from various officials, including federal judges and politicians, including former New York Gov. George Pataki. Nadler did not mention impeachment in the statement announcing the hires, but noted that Trump faces “numerous allegations” of corruption and obstruction.

Democratic lawmakers have said they are somewhat limited in what they can do because they don’t have the ability to conduct a criminal investigation as Mueller does. So they say access to Mueller's final report will be significant.

Iowa Republican Sen. Chuck Grassley said last week he expects the Mueller report to be produced "within a month," although he later said he was merely repeating reports and speculation. Nadler and other Democrats have pressured Trump’s nominee for attorney general, William Barr, to release as much of that report as possible.

Meanwhile, the House intelligence committee is also preparing a broad investigation into Trump’s finances and foreign connections and has added new staff with experience at the National Security Council. One of them, Abigail Grace, worked for both Trump and former President Barack Obama on the NSC.

In response, Trump excoriated the House intelligence committee chairman, Adam Schiff, D-Calif., last week.

"He has no basis to do that. He’s just a political hack who’s trying to build a name for himself,” Trump said. “It’s just presidential harassment and it’s unfortunate, and it really does hurt our country."

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Trump, who last November called Schiff "little Adam Schitt," warned during his State of the Union that an "economic miracle is taking place in the United States -- and the only thing that can stop it are foolish wars, politics or ridiculous partisan investigations."

“Looks like Democrats are staffing up for impeachment before Mueller’s report is even out,” Collins said.

The Associated Press contributed to this report.