The president tweeted, "Again, the story that there was collusion between the Russians & Trump campaign was fabricated by Dems as an excuse for losing the election".
Another former high-ranking Federal Bureau of Investigation official said the threat of getting fired could be enough to keep agents from digging into Trump's ties to Russian Federation.
After being told of Comey's controversial handling of the investigation into Hillary Clinton's private email server, 47% of all voters - 70% of Republicans and 29% of Democrats - thought it was appropriate to fire him. Both polls have a margin of error of plus or minus 2 percentage points.
President Trump threatened Friday morning to end White House press briefings, arguing that "it is not possible" for his staff to speak with "perfect accuracy" to the American public.
Mr Trump's outburst came amid growing scrutiny over the White House's account of how Mr Comey was sacked, particularly its initial claim that Mr Trump had only fired him on the recommendation of his new deputy attorney-general Rod Rosenstein - a claim that Mr Trump laid out in his letter of dismissal.
The No. 2 Democrat in the Senate, Richard Durbin, slammed the President after Friday's tweets, telling MSNBC that the President is "dangerous because he may be obstructing justice in terms of the investigation. and secondly his credibility has been destroyed".
Comey told Trump he would be "honest" with him, to which, according to the published account, Trump asked if it could "honest loyalty".More news: Syrian Kurdish forces to push on IS capital this summer
In addition to the Friday morning tweet barrage, Trump called Comey, who was leading the FBI's Russian Federation probe, a "showboat" and "grandstander" in the NBC interview, and contradicted the timeline of the firing outlined by his aides and Vice President Michael Pence. The Clinton investigation was closed in early November, and Mr Trump has been in office since 20 January.
The issue is unlikely to go away, however, especially in light of Trump's tweet on Friday implying that the conversation had been recorded. "As a very active President with lots of things happening, it is not possible for my surrogates to stand at podium with ideal accuracy!" "Maybe the best thing to do would be to cancel all future "press briefings" and hand out written responses for the sake of accuracy???"
Democratic former presidential contender Bernie Sanders also highlighted the fact the decision came a day after former Acting Attorney General Sally Yates told a Senate committee of the concerns she had over Mr Flynn's Russian Federation ties.
Clapper's remarks came amid fallout from Trump's interview with NBC's Lester Holt Thursday. But Trump on Thursday acknowledged for the first time that the Russian Federation investigation - which he dismissed as a "made-up story" - was also on his mind as he ousted the man overseeing the probe.
"I was going to fire regardless of [his] recommendation", Mr Trump told NBC. Then at least one possibly credible body not subject to the president's discharge power would be on the hunt for the real story of why Trump fired the main investigator on his trail and precisely what he has been trying to hide.
The firing of Comey already has left Trump with the dubious distinction of being the first president since Nixon to dismiss a law enforcement official overseeing an investigation tied to the White House. Mr Trump has repeatedly refused to release his tax returns, making it impossible to verify the conclusions.
It hardly needs saying that this explanation, if true, would necessarily lead to the impeachment, conviction and removal of President Trump - assuming the requisite political backbone on the part of the House and Senate.