Of 49 headline-grabbing events during the Trump administration, the panelists have said most were at least somewhat important, with about half normal and half abnormal.

Other events they have said were also highly important and abnormal — though none as important as Mr. Comey’s firing — were the administration’s use of terms like “alternative facts” and “fake news”; its continued attacks on news organizations; Mr. Trump’s false accusation that President Obama wiretapped him; the White House’s decision to give its staff members secret waivers to its own conflict-of-interest rules; and the F.B.I.’s Russia investigation. The wiretapping claim was the most abnormal event to date, they said.

A couple of experts noted that Mr. Trump had authority to fire Mr. Comey. Saikrishna Prakash, a professor of law at the University of Virginia, said it was no surprise, but what made it unusual was that he waited so long. “The decision is somewhat unusual because Trump could have ousted Comey at the outset and failed to do so, in the face of much evidence that the F.B.I. needed new leadership,” he said.

Thomas Nichols, a professor at the U.S. Naval War College, also said it was only moderately abnormal, but that the way Mr. Trump chose to do it was unusual. “It’s within the president’s powers, and given how many times people in both parties called for Comey to be fired, hard for people to act surprised that it finally happened,” he said. “Amazingly, the administration managed to look suspicious doing it anyway.”

Most of the experts found it much more significant and abnormal. Jennifer Hochschild, chairwoman of the department of government at Harvard, called it “deeply alarming.” Frances Lee, a professor of government and politics at the University of Maryland, said, “There’s no parallel.”

Many of the experts said the action raised concerns about checks and balances in American democracy, involving the Russia investigation and more broadly.

Tom Ginsburg, a professor of comparative and international law at the University of Chicago, said even if the investigation continued, the move could undermine the results. “Given the fact that the F.B.I. was actively engaged in an investigation of the president’s campaign contacts with foreign powers, firing the director undermines the credibility of any pro-Trump results,” he said.