POLITICAL TENSION is running high in the United States, extraordinarily so, we’d say. And so it behooves everyone in a position of official responsibility to do everything he or she possibly can to help maintain stability — while avoiding all avoidable provocations — until the bitter competition between Hillary Clinton and Donald Trump runs its ugly course on Nov. 8.

That is the context for Friday’s announcement by James B. Comey, director of the Federal Bureau of Investigation, that his agency is again looking into Ms. Clinton’s private email server in light of newly discovered emails “that appear to be pertinent to the investigation.” Mr. Comey may have had good reason to inform Republican committee chairmen in Congress of the review, but his timing was nevertheless unfortunate, given its potential to affect a democratic process in which millions of people are already voting.

[James Comey fails to follow Justice Department rules yet again]

What might his reason be? On the merits, Ms. Clinton erred by using a private email server for her official communications as secretary of state — though as we have previously argued, the matter has been greatly overblown. According to the previous FBI review, the small amount of classified material that moved through Ms. Clinton’s private server was not clearly marked as such, and no harm to national security has been demonstrated.

The FBI conducted a thorough investigation for any prosecutable offenses, especially any involving the transmission of classified information. Mr. Comey rightly recommended against bringing charges; he told his staff that the decision was “not a cliff-hanger.” In deference to the reality that the target of the inquiry was a major-party nominee for president, he gave the public a summary of the facts and law behind his decision.

Democratic presidential candidate Hillary Clinton spoke to reporters Oct. 28 in Des Moines about the FBI's new inquiries into the private email server she used as secretary of state. (The Washington Post)

Mr. Comey went too far, however, in providing raw FBI material to Congress, notwithstanding its important oversight role; that attempt to appease Republicans set a precedent that future partisans who are unhappy with the results of FBI investigations may exploit.

Mr. Comey found himself in a bind when his investigators turned up additional, previously unexamined Clinton emails, apparently on devices belonging to top aide Huma Abedin and her husband, Anthony Weiner, seized during an FBI probe of the latter’s alleged sexual misconduct with a minor. (As if this could not get any more bizarre.) If Mr. Comey failed to tell Congress before Nov. 8 about his decision to review them, he would be accused — again — of a politically motivated coverup. By revealing it, he inevitably creates a cloud of suspicion over Ms. Clinton that, if the case’s history is any guide, is unwarranted. Hence Clinton campaign chairman John Podesta’s not unreasonable demand that Mr. Comey “immediately provide the full details of what he is now examining.”

[James Comey needs to clean up his mess. Here’s what we need to know.]

Mr. Podesta said he is “confident” full disclosure “will not produce any conclusions different from the one the FBI reached in July.” If so, the question will be how badly damaged was Ms. Clinton’s candidacy by the 11th-hour re-eruption of a controversy that never should have generated so much suspicion or accusation in the first place.