Former Director of National Intelligence James Clapper described Sunday a U.S. government “under assault” after President Trump’s decision to fire FBI Director James Comey.

"I think, in many ways, our institutions are under assault, both externally -- and that's the big news here, is the Russian interference in our election system," Clapper said in a televised interview with CNN. "I think as well our institutions are under assault internally."

When he was asked, "Internally, from the president?" Clapper said, "Exactly."

Clapper’s comments came after Trump’s sudden firing of Comey last week, which drew sharp criticism because it came amid the FBI’s probe into Russia meddling in the 2016 presidential election and possible ties between Russia and Trump’s presidential campaign.

Clapper said America's founding fathers had created three co-equal branches of government with checks and balances, but with Trump as president, that was now "under assault and is eroding."

Trump abruptly fired Comey on Tuesday and later said Comey was a “showboat” and a “grandstander” who was not doing a good job. Trump said in an interview with NBC that the investigation factored into his decision to fire Comey. The changing rationales the White House offered added an element of chaos to the president's action.

Sen. Lindsey Graham, R-S.C., said in a televised interview on NBC that Trump should hire an FBI agent who would allow the nation to “reset.” He dismissed as less desirable at least two of the 14 candidates under consideration by Trump, former Rep. Mike Rogers of Michigan and Sen. John Cornyn of Texas, explaining that "these are not normal circumstances."

"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," Graham said. Asked whether Rogers or Cornyn would be good choices, Graham flatly said, "no."

"The president has a chance to clean up the mess he mostly created," Graham said, adding, "I have no evidence the president colluded with the Russians at all, but we don't know all the evidence yet."

The administration has interviewed at least eight candidates to be FBI director, and Trump has said a decision could come before he leaves Friday on his first overseas trip as president.

The Associated Press contributed to this report.