Reporting by Margaret Brennan.
House Republicans have asked for their own impeachment witnesses Saturday and submitted a list that includes the anonymous whistleblower who filed the complaint that has triggered an impeachment inquiry into President Trump over his July 25th call with Ukrainian President Volodymyr Zelensky.
Among those requested to be witnesses for public hearings as part of the GOP-led effort included former Vice President Joe Biden's son, Tim Morrison, and Kurt Volker -- all key players in the current probe against Mr. Trump. The president weighed in on the list of would-be witnesses, tweeting Saturday that House Speaker Nancy Pelosi, Congressman Adam Schiff and Joe Biden be added to the list.
An attorney for the whistleblower responded to the request in an email to CBS News that he was concerned Republicans were attempting to "unmask" his client's identity, calling for Nunes to honor his past support for the lawful protection of all government whistleblowers.
"I urge all of our government leaders - notably all Members of Congress - to step back and reflect on the important role whistleblowers play in our constitutional republic's ability to oversee itself," the letter reads.
It adds, "Members of the Intelligence Community, whether they are federal employees or government contractors, must follow the law in disclosing their reasonable belief of a violation of law, rule, regulation, or an abuse of authority. Failure to do so would mean that the unauthorized public disclosure of classified information could cause grave harm to our national security."
Schiff sent a letter to House Intelligence Committee Ranking Republican, Congressman Devin Nunes, on Saturday, saying he will give due consideration to witnesses within the scope of the impeachment inquiry," but the whistleblower's testimony is "redundant and unnecessary."
"In light of the president's threats, the individual's appearance before us would only place their personal safety at grave risk," Schiff wrote in the letter, which CBS News has obtained.
Andrew Bakaj, the attorney who sent a letter to Nunes, also released a series of letters he and his co-counsel Mark Zaid had previously sent to Nunes over the last few weeks, including two separate offers to have the whistleblower answer Republicans' questions in writing. Those offers, however, have gone unanswered since the first one made on November 2 and again on the 6th.
Nunes' office did not immediately respond to a request for comment by CBS News.
Bakaj, however, told CBS News that publicly identifying the whistleblower will "fundamentally harm a process that took decades to build" and the consequences could be "long-lasting."
"If Congress and others do not protect my client's anonymity — which my client is afforded to by law — not only does it jeopardize their safety, but it jeopardizes an entire system that took decades to build. It will destroy effective Congressional oversight for years to come," Bakaj said.
Bakaj cited a previous report by The Daily Beast that said Nunes had previously supported protecting the anonymity of whistleblowers.
"Members of the Intelligence Community, whether they are federal employees or government contractors, must follow the law in disclosing their reasonable belief of a violation of law, rule, regulation, or an abuse of authority," the letter said. "Failure to do so would mean that the unauthorized public disclosure of classified information could cause grave harm to our national security."
last week that he contacted Nunes to say his client is willing to answer Republicans' questions under oath and penalty of perjury if lawmakers submitted written questions to the whistleblower's legal team. The inspector general of the intelligence community, an appointee of Mr. Trump, could verify the whistleblower's identity to satisfy the committee's minority members while protecting the individual's anonymity.
Previously, the whistleblower had offered to answer questions under oath and in writing if submitted by the House Intelligence Committee as a whole. Zaid's offer would be a direct channel of communication with the Republicans who are in the minority on that committee. Republican leadership has complained that the process is unfair and overly restrictive on their ability to question witnesses.
House Intelligence Committee Chairman Adam Schiff told "Face the Nation" last month the whistleblower's testimony may no longer be needed.
"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 October 13, referring to the July 25 call between President Trump and the Ukrainian president. "We have the best evidence of that."
Mr. Trump said Saturday that a transcript of another call he had with the president of Ukraine will "probably" be released on Tuesday. The call took place in April after Zelensky was elected.