"I don't think - that's not a threat".
Pressed by anchor Jake Tapper if he meant United States institutions were under assault internally from the President, Clapper responded, "Exactly".
"The founding fathers, in their genius, created a system of three co-equal branches of government and a built-in system of checks and balances", Clapper said.
US Vice President Mike Pence said the firing had nothing to do with the FBI's Russian Federation probe, but Trump dismissed the claim in his NBC News interview on Thursday.
"If that's accurate, I'm hearing that it's not - to say that we would have some concern would be accurate, that would be troubling", Walker told CNN.
The White House would not confirm or deny if there are listening devices in the Oval Office.
Trump also tweeted Friday morning that "maybe the best thing to do would be to cancel all future "press briefings" and hand out written responses for the sake of accuracy", a remark he made after contradicting his press aides and other surrogates on his reasons for firing Comey earlier in the week. "The exchange that took place with Comey, whichever version you believe, raises very, very serious questions about attempts to pressure an FBI director investigating wrongdoing potentially implicating the president".
Republican Senator Lindsey Graham, a member of the Judiciary Committee, said promoting an Federal Bureau of Investigation agent to lead the agency would allow the nation to "reset". Comey, for instance, was a former United States attorney in Manhattan before being appointed deputy attorney general by George W. Bush.
Mr Rogers, an ex-FBI agent and former chairman of the House Intelligence Committee, has drawn the backing of the FBI Agents Association.
"It's now time to pick somebody who comes from within the ranks, or is of such a reputation who has no political background at all who can go into the job from Day 1", the South Carolina Republican said.
"The president has a chance to clean up the mess he mostly created", he said, adding, "I have no evidence that the president colluded with the Russians at all. but we don't know all the evidence yet".
In this photo taken May 8, 2017, FBI Director James Comey speaks in Washington.
Democratic lawmakers - including New Jersey Sen. When the opposite occurred, Trump grew incensed - both at Democrats and his own communications staff for not quickly lining up more Republicans to defend him on television. Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee, said his panel or another committee would "absolutely" subpoena the tapes. "Then that would have been the big story as opposed to the inauguration", Trump said.
"I expect nothing short of someone beyond reproach and (it) will be exactly what the country needs", said Warner, a Trump delegate at last year's party convention.
Party leaders said Trump was right to fire Comey, or at least that he had a right to do it. The appointment Wednesday followed news of Comey's memo saying that Trump had asked him to shut down the FBI's investigation into ousted National Security Adviser Michael Flynn and his Russian Federation ties.
The president also suggested via Twitter that he may have "tapes" of private conversations with Comey, evoking echoes of Watergate and demands by Democrats that he produce what could be critical evidence.
So far 14 people have emerged as candidates. Ms Fisher formerly served as assistant attorney general for the Justice Department's Criminal Division.
Sources close to Deputy Attorney General Rod Rosenstein say he is not in favor of appointing a special prosecutor to investigate Russia's alleged involvement in the 2016 presidential election.