Senate Republicans say they will call former senior Obama officials to testify about their multiple requests to "unmask" former Trump national security adviser Michael Flynn’s identity on intercepted calls with former Russian Ambassador Sergey Kislyak.

Atop the list of former senior Obama administration officials that GOP senators want to hear from are former Director of National Intelligence John Clapper, former CIA Director John Brennan, former Obama White House chief of staff Denis McDonough and, possibly, former Vice President Joe Biden.

“Right now we’re in the information gathering phase of this and this obviously, from my standpoint, raises a lot more questions than it actually answers,” Senate Homeland Security Committee Chairman Ron Johnson (R-Wis.) told reporters Wednesday.

Johnson said “we will start requesting interviews with those individuals.”

“I want to find out what you were looking at, why you unmasked an American’s identity and how you used that,” he added.

Asked who he most wants to hear from, Johnson pointed to Clapper, Brennan, McDonough and “possibly the vice president.”

Johnson said he is most interested in finding out who leaked information about Flynn’s intercepted conversations with Kislyak during President Trump’s transition to office after the 2016 election.

He called it “a campaign to sabotage this administration.”

“It is outrageous what these officials from the Obama administration did to the incoming administration,” he added. “We’ll pick the ones to get the information.”

Johnson said he wanted to compare dates of unmasking requests related to Flynn’s conversations with Kislyak and stories that surfaced at the time in the media.

“We need to try to piece this altogether,” he added.

Johnson requested information from former Inspector General of the Intelligence Community Michael Atkinson in October about if he had investigated leaks of sensitive information from the intelligence community regarding its investigation of Trump’s 2016 presidential campaign.

Sen. Rand Paul (R-Ky.) on Wednesday afternoon called on Biden, Clapper, Brennan and former FBI Director James Comey to testify.

“The Senate must immediately hold hearings on this! Clapper, Comey, Brennan and even Biden owe it to the American people,” he tweeted. “They should testify under oath. What did the former president know?”

Paul earlier floated the idea of having acting Director of National Intelligence Richard Grenell testify before his Federal Spending Oversight and Emergency Management Subcommittee of the Homeland Security Committee next week about the unmasking process.

Johnson, the chairman of the Homeland Security panel, however, said Wednesday that Grenell’s appearance is unlikely.

Grenell on Wednesday shared declassified documents with Senate Republicans revealing that 39 senior Obama administration officials, including Biden, Clapper, Brennan, McDonough and Comey had requests made in their name to unmask Flynn’s identity on the transcripts of intercepted calls with Kislyak.

The requests were made between Election Day 2016 and Jan. 31, 2017, eleven days after Trump’s inauguration.

Paul at a press conference Wednesday said Biden has been caught “red-handed’ eavesdropping on Trump’s presidential transition team.

Paul said investigators need to find out “what did President Obama know and when did he know it.”

He said former Obama administration officials need to be asked whether they disclosed information about Flynn’s conversations with Kislyak and what he advised them to do with it.

Paul said there have been rumors for years that Obama’s administration was abusing the power to unmask the identities of Americans whose communications with foreign individuals are captured by U.S. intelligence agencies, primarily the National Security Agency.

“It looks like each of these administration officials actually individually requested to listen to this conversation,” he said.

“This is Vice President Biden using the spying powers of the United States to go after a political opponent. He’s caught red-handed here,” Paul added. “That to me is alarming.”

Flynn briefly served at Trump’s national security adviser before resigning in February 2017 after it was reported that he had misled Vice President Pence and other officials about his conversations with Kislyak.

Flynn was later charged with lying to an FBI agent in a criminal case the Department of Justice dropped last week.

Senate Judiciary Committee Chairman Lindsey Graham (R-S.C.) said he plans to hold a hearing in June on possible political interference in the FBI’s and the Department of Justice’s decisions to investigate and prosecute Flynn.

“I don’t think they have any business at all surveilling the incoming national security adviser,” he said. “If they’re surveilling me, wanting to know what I’m telling [Israeli Prime Minister Benjamin] Bibi [Netanyahu] about foreign policy, it would bug the shit out of me. I think the whole thing sucks.”

Sen. Chuck Grassley (R-Iowa) said Johnson and Graham would take the lead in holding hearings on Flynn and what actions members of the Obama administration took to set up his prosecution.  

“My team intends to follow it where the facts lead us and right now all we have is names, we don’t have any facts. We’ll pursue that,” he said.

Grassley along with Johnson and Paul on Thursday released the declassified documents from the Office of the Director of National Intelligence showing repeated requests by senior Obama administration officials to unmask Flynn.

He predicted Grenell’s disclosure would spur investigative reporting by the press, as well.

“You got to see this as part of a bigger picture,” he said. “For three years we’ve had everything stalled because somebody had a big excuse because they didn’t want any of this information coming out.”

Grassley said that former Director of National Intelligence Dan Coats, who served under Trump, had held up information that he had requested.