The House Intelligence Committee on Wednesday issued subpoenas to former White House National Security Adviser Michael Flynn, President Trump's personal business attorney Michael Cohen as well as former Obama administration officials Susan Rice, Samantha Power and John Brennan.
The Senate Intelligence Committee said on Thursday it would hear from Comey, who was sacked by Trump on May 9, first in an open session and then behind closed doors, which would afford senators a chance to discuss classified information.
These are the first subpoenas to come from the panel, issued by Chairman Rep. Mike Conaway and ranking member Rep. Adam Schiff.
Schiff feels that Rep. Mike Conaway, R-Texas, who is filling Nunes' role as head of the Russian Federation investigation, is the person who should have that authority.
So far, Rice has not denied unmasking Trump associates, and former Director of National Intelligence James Clapper admitted to doing so during a hearing last month.
Public testimony by the former FBI director could mark another major development in the controversy engulfing the Trump administration about past contacts with Russian officials - and whether the president or White House officials took steps to try to squelch the investigation. He also blasted Nunes for "unilaterally" issuing the three subpoenas related to unmasking requests. Conaway later said that the Russian intelligence Nunes saw was not related to the House investigation.
"You often couldn't understand what was going on unless you asked for the identity of the US persons", once former official told Foreign Policy. The sources declined to say whether those requests originated with Republican or Democratic committee members, but said committee rules require the chairman to sign off on such requests.
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The California Republican supposedly stepped aside from the House Intelligence Committee's Russian Federation investigation. President Trump has argued that the leaks should be the focus of the investigation.
The subpoenas asked the agencies to provide details of any requests made by two top Obama administration aides and the former CIA director to "unmask" names of Trump campaign advisers inadvertently picked up in top-secret foreign communications intercepts, congressional sources said.
"Seeing a lot of fake news from media elites and others who have no interest in violations of Americans' civil liberties via unmaskings", Nunes tweeted.
While Nunes remains the chairman of the House Intelligence Committee, he has removed himself from the committee's highest profile effort, investigating the Russian meddling in the 2016 election and the possible collusion of the Trump campaign.
Separately, federal prosecutors pursuing a criminal investigation into Flynn have issued subpoenas to people and businesses who have done business with him seeking information, including bank records and communications, related to Flynn, the Flynn Intel Group and Invovo BV, a Dutch company owned by Turkish businessman Ekim Alptekin, according to a document reviewed by Reuters.
The Associated Press reported earlier this month that Comey planned to testify before the Senate committee after Memorial Day, but the approval from Mueller to do so could indicate that date is fast approaching.
"I think the agencies are cooperating with us and have not attempted to withhold any information from us", he said.