The Clinton campaign and its supporters are apoplectic. But top federal law enforcement officials from both Democratic and Republican administrations have been just as swift and fierce in their condemnation of Mr. Comey. The Justice Department, of which the F.B.I. is a part, has a longstanding rule against disclosing inflammatory information to the public and even to Congress about an investigation within 60 days of an election, because that might be seen as influencing the vote.

Eric Holder Jr., the former attorney general, wrote in The Washington Post that Mr. Comey had “committed a serious error with potentially severe implications” and that he had “negatively affected public trust” in the Justice Department and the F.B.I. Alberto Gonzales, who was attorney general under President George W. Bush, said, “To throw out this kind of letter without more information, without really knowing what the facts are with respect to these additional emails, I think was a mistake.”

Richard Painter, President Bush’s top ethics lawyer from 2005 to 2007, went further, saying Mr. Comey’s letter had “very likely” violated a federal law barring public officials from using their position to influence the outcome of an election. In an op-ed essay in The Times, Mr. Painter said he had filed a complaint with the Office of Special Counsel to investigate Mr. Comey’s action.

Harry Reid, the Senate minority leader, echoed that charge in a letter to Mr. Comey and also criticized what he labeled a double standard. He has called on the F.B.I. to release information about any investigation into Donald Trump’s ties with the Russian government, too. But that would only compound the damage Mr. Comey has done, violate the Justice Department’s rule and further politicize the F.B.I.

Mr. Comey appears to have grasped the importance of that rule in some contexts. On Monday, CNBC reported that in early October, Mr. Comey fought successfully to keep the F.B.I.’s name off a government report regarding evidence that Russia was attempting to interfere in the presidential election. He believed the report was accurate but did not want to sign on to it so close to the election.