Washington - American democracy is separately "under assault" from President Donald Trump and Russia, the former US intelligence chief warned on Sunday, expressing dismay over the abrupt firing of FBI director James Comey amid a probe into Moscow's meddling in US elections and possible ties with the Trump campaign.As Trump works to fast-track Comey's successor, lawmakers from both parties urged him to steer clear of any politicians for the job and say he must "clean up the mess that he mostly created"."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," said James Clapper, the former director of national intelligence. "I think as well our institutions are under assault internally."When he was asked, "Internally, from the President?" Clapper said, "Exactly."Clapper spoke following Trump's sudden firing of Comey last week, which drew sharp criticism because it came amid the FBI's investigation into Russia's interference in the 2016 presidential election. 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 "eroding".The White House had no immediate comment on Clapper's remarks on a morning in which no White House aide appeared on the Sunday news shows to discuss Comey's firing.'Tapes'Lawmakers from both parties reprimanded Trump's actions last week, which included shifting explanations from the White House for Comey's dismissal and an ominous tweet by Trump that warned Comey against leaks to the press because he may have "tapes" of their conversations. The lawmakers urged Trump to select a new FBI director without any political background and said the president would need to hand over to Congress any taped conversations with Comey, if they exist.Republican Senator Lindsey Graham, a member of the Judiciary Committee, said promoting an FBI agent to lead the agency would allow the nation to "reset". He dismissed as less desirable at least two of the 14 candidates under consideration by Trump, Mike Rogers and Senator John Cornyn of Texas, explaining that "these are not normal circumstances".Rogers, an ex-FBI agent and former chair of the House Intelligence Committee, has drawn the backing of the FBI Agents Association. Cornyn is the No. 2 Republican in the Senate."It's now time to pick somebody who comes from within the ranks, or has such a reputation that has no political background at all that can go into the job on Day 1," the South Carolina Republican said. Asked whether it was the right time to have someone such as Rogers or Cornyn, Graham flatly said, "no"."The President has a chance to clean up the mess he mostly created," Graham said, adding, "I have no evidence that the president colluded with the Russians at all ... but we don't know all the evidence yet."'Courage'Senate Minority Leader Chuck Schumer of New York said the new FBI director should certainly be someone "not of partisan background" with "great experience" and "courage".He left open the possibility that Democrats might try and withdraw support for a new FBI director unless the Justice Department names a special prosecutor. Under rules of the Senate, Republicans could still confirm an FBI director with 51 votes. Republicans hold 52 seats in the chamber to Democrats' 48.Calling Trump's remarks about possible taped conversations "outrageous," Senator Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee, said his panel or another congressional committee would "absolutely" subpoena the tapes."We have got to make sure that these tapes, if they exist, don't mysteriously disappear," he said.Warner also said he hopes to have Comey testify in a public hearing before his committee. Comey earlier declined an invitation this week to testify in a closed hearing.Less than a week after Trump fired Comey, the administration has interviewed at least eight candidates to be FBI director, and Trump has said a decision could come before he leaves on Friday on his first overseas trip as president.Trump abruptly fired Comey on Tuesday and later said Comey was a "showboat" and "grandstander" who was not doing a good job, drawing a firestorm of criticism. Trump said in an interview with NBC that the Russia 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.The FBI director serves a 10-year term, but can be replaced by the president.14 candidatesSo far 14 people - lawmakers, attorneys and law enforcement officials among them - have emerged as candidates. Eight met at the Justice Department on Saturday with Attorney General Jeff Sessions and his deputy, Rod Rosenstein.Sessions has faced questions over whether his involvement in Comey's firing violates his pledge to recuse himself from investigations into Russian interference in the election.Justice Department spokesperson Sarah Isgur Flores said Sessions and Rosenstein were involved in the interviews because the FBI director reports to them as attorney general and deputy attorney general.