House Intelligence Committee Ranking Member Devin Nunes (R-Calif.) has sent a formal letter to Committee Chairman Adam Schiff (D-Calif.), requesting that Schiff testify behind closed doors as to the nature of his conversations with the whistleblower whose complaint catapulted House Democrats' impeachment probe against President Donald Trump.

What are the details?

In the letter obtained by Fox News, Nunes calls on Schiff to sit before the House Intelligence, Foreign Affairs, and Oversight Committees in a private setting, urging the chairman to provide testimony and telling him, "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."

Schiff initially said neither he nor his staff had direct contact with the whistleblower, but later walked back that claim and admitted to providing guidance to the individual. As Nunes has indicated, Schiff also promised to allow the whistleblower to give private testimony to Congress as part of the impeachment investigation, and then decided such testimony was no longer necessary.

Nunes addressed Schiff's about-face on allowing Republican members to question the whistleblower, writing in his letter to the chairman, "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 Washington Examiner noted that "Schiff has been under scrutiny from Republican lawmakers who feel that his efforts to impeach Trump have been molded by a partisan interest as a Democrat in removing the president from office." Last month, dozens of House Republicans stormed into a private impeachment hearing in the basement of the Capitol, after being barred by Chairman Schiff.

Anything else?

An unnamed GOP source told Fox News it's unlikely that Schiff — who is leading the impeachment proceedings — would comply with Nunes's request.

The operative added that Republicans would like to know: "How many times did (Schiff) meet with the whistleblower? What did they advise the whistleblower to do? How much was Schiff involved in this? Did he recommend the whistleblower give the complaint to the intelligence community inspector general, even though there was no intel component so that he could be involved?"