Washington — The top Republicans on the House committees pursuing the impeachment inquiry are demanding the public testimony of the whistleblower who reported concerns about President Trump's dealings with Ukraine, as well as other officials referenced in the individual's complaint, according to a letter obtained by CBS News.

The request is the first time Republican lawmakers involved in the impeachment probe have formally asked Democrats to call witnesses, a possible indication they intend to pursue more traditional channels to counter the investigation even as members seek to disrupt the proceedings themselves.

Republicans Jim Jordan, Devin Nunes and Michael McCaul wrote a letter on Wednesday to Democrat Adam Schiff, the chairman of the House Intelligence Committee, demanding to hear from the whistleblower, an employee in the intelligence community whose identity remains unknown.

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"As the so-called impeachment inquiry gathers information that contradicts the employee's allegations, we ask that you arrange for the committees to receive public testimony from the employee and all individuals he or she relied upon in formulating the complaint," the lawmakers wrote. As members of the minority, House Republicans do not have the authority to call witnesses themselves, unless given the power to do so by the Democratic majority.

Read the full letter here

The whistleblower's August 12 complaint about Mr. Trump's July 25 call with Ukrainian President Volodymyr Zelensky kicked off a series of events that led Democrats to open the impeachment inquiry in September. The individual cited conversations with a number of White House officials who expressed concerns about the call.

In their letter Wednesday, the Republican leaders claim the whistleblower's complaint was contradicted by the official summary of the call, since the summary "contains no reference to the 2020 presidential election." However, the summary shows Mr. Trump encouraged Zelensky to "look into" former Vice President Joe Biden and his son, Hunter. Subsequent testimony by U.S. officials has revealed a concerted effort by Mr. Trump and U.S. diplomats to get Ukraine to announce it was opening investigations into the Bidens and supposed Ukrainian interference in the 2016 elections.

The ranking members said they want to hear from the whistleblower to "fully assess the sources and credibility of the employee."

Republicans have sharply criticized Democrats over the process by which they are conducting the impeachment inquiry, decrying the use of closed-door hearings and alleged selective leaking of witness testimony.

"Several witnesses have offered closed-door testimony in this so-called impeachment inquiry that rebuts the central assertion of the anonymous employee's complaint," the ranking members wrote in their letter to Schiff. A spokesman for Schiff declined to comment.

On Wednesday, two dozen GOP lawmakers delayed the deposition of a key witness for more than five hours, staging a sit-in in a secure hearing room to protest a lack of access to interviews and investigatory material. (Some of the members involved in the demonstration are members of the committees and already have access to the material.) Several lawmakers carried cellphones into the secure room, known as the SCIF, in apparent violation of security protocols.

Democrats have largely dismissed Republicans' concerns and insisted the closed-door process is necessary to protect the integrity of the investigation and prevent witnesses from coordinating their stories.

Schiff initially said Democrats were working to arrange for the whistleblower to testify, but seemed to back off that position in an interview with "Face the Nation" two weeks ago, saying additional evidence has since corroborated the whistleblower's account.

"Given that we already have the call record, we don't need the whistleblower, who wasn't on the call, to tell us what took place during the call," Schiff said on October 13. "We have the best evidence of that."

Democrats have also expressed concerns about protecting the identity of the whistleblower during potential testimony, and at one point considered concealing the individual's voice or appearance.

Mr. Trump has repeatedly suggested that he wants to know who the whistleblower is.

"Where's the Whistleblower?" Mr. Trump tweeted Wednesday morning.