Rep. Devin NunesDevin Gerald NunesNunes demands Schiff testify behind closed doors in Trump impeachment inquiry Democrats aim to impeach Trump by Christmas Schiff says GOP must prove relevance for impeachment hearing witnesses MORE (R-Calif.), the top Republican on the House Intelligence Committee, has formally requested that Rep. Adam SchiffAdam Bennett SchiffNunes demands Schiff testify behind closed doors in Trump impeachment inquiry Democrats aim to impeach Trump by Christmas Schiff told Gaetz to 'absent yourself' in fiery exchange: impeachment transcript MORE (D-Calif.), the chairman of the panel, privately testify as part of the House’s impeachment investigation into President TrumpDonald John TrumpKey impeachment witnesses to know as public hearings begin Centrist Democrats seize on state election wins to rail against Warren's agenda Nunes demands Schiff testify behind closed doors in Trump impeachment inquiry MORE.

In a letter to Schiff, which was obtained and released by Fox News, Nunes wrote that the Intelligence Committee should not be conducting a "show trial" impeachment inquiry.

"On November 6th, you announced the beginning of public hearings associated with the Democratic Party's partisan impeachment inquiry into President Donald J. Trump," Nunes wrote Friday.

"Based on the precedent and lack of jurisdiction, the House Intelligence Committee should not take the lead in conducting such hearings; however, by now the American people know your desire to see the duly-elected president removed from office outweighs your sense of responsibility to running a functioning intelligence oversight committee," he continued.

"Prior to the start of your public show trial next week, at least one additional closed-door deposition must take place," he added. "Specifically, I request that you sit for a closed-door deposition before the House Intelligence, Foreign Affairs and Oversight Committees." 

Schiff has emerged as a top target for Trump’s allies on Capitol Hill, with many saying the White House has been robbed of due process. 

The House’s impeachment probe was launched in September after a whistleblower raised alarms over Trump’s dealings with Ukraine. Democrats have expressed fears that Trump leveraged $400 million in military aid to Ukraine to pressure Kiev to investigate former Vice President Joe BidenJoe BidenCentrist Democrats seize on state election wins to rail against Warren's agenda Nunes demands Schiff testify behind closed doors in Trump impeachment inquiry Chris Hayes and his audience troll Trump: 'Yes, Read the Transcript!' MORE, a chief political rival. 

Several witnesses have since testified that they believed there was a quid pro quo involved in Trump’s dealings with Ukrainian President Volodymyr Zelensky.

Republicans have seized on the fact that Schiff was aware there was a whistleblower, with whom his staff interacted. However, Schiff has said he did not know anything about the person’s complaint prior to its filing.

"Although you publicly claim nothing inappropriate was discussed, the three committees deserve to hear directly from you the substance and circumstances surrounding any discussions conducted with the whistleblower, and any instructions you issued regarding those discussions," Nunes wrote. "Given that you have reneged on your public commitment to let the committees interview the whistleblower directly, you are the only individual who can provide clarity as to these conversations."

The letter indicates that Republicans intend to continue focusing on the investigation's process as a means of defending Trump, even as multiple witnesses expressed misgivings about Trump’s interactions with Zelensky.