Correction: An earlier version of this editorial incorrectly reported Harry Reid’s (D-Nev.) leadership position in the Senate. He is the minority leader. This version has been corrected.

NO ONE SHOULD be happy that the outcome of a U.S. presidential election could be affected, if not determined, by a cryptic letter from the FBI director released 11 days before the vote. But that is our unfortunate situation. So what do we do now?

For starters: Take a deep breath. Remember what is important and what is not. And, modifying the Hippocratic oath: Do no further harm.

What would that mean? For Republican nominee Donald Trump, it would mean not lying about what has happened. The email affair is not “bigger than Watergate.” The Democratic nominee for president, Hillary Clinton, does not belong in prison. But preposterous hyperbole and lying are Mr. Trump’s bread and butter. A candidate who whines about “rigged” polls when they show him losing; who carelessly spreads conspiracy theories about shadowy global bankers plotting to seize U.S. sovereignty; who debases the process by labeling his opponent “crooked” — such a man will exploit a situation like this irrespective of any harm he might cause to American democracy. That is par for his course.

For Ms. Clinton and the Democrats, doing no harm would mean not imputing base motives to FBI Director James B. Comey or absurdly alleging, as did Senate Minority Leader Harry Reid (D-Nev.), that Mr. Comey may have violated the Hatch Act by intentionally seeking to get Mr. Trump elected. For one thing, such allegations sound silly coming from people who practically canonized Mr. Comey a few months ago when he announced that there were no grounds to prosecute Ms. Clinton. For another, whatever the wisdom of Mr. Comey’s actions, there is no basis for such allegations, as President Obama’s spokesman said Monday.

The Post’s Matt Zapotosky explains why FBI Director James B. Comey has found himself at the center of the presidential campaign in recent days. (Bastien Inzaurralde/The Washington Post)

What about Mr. Comey himself? Is there anything he can do to mitigate the harm that has been caused? In July, he cited transparency as a goal, yet in this go-round he has offered voters little guidance. Much of what we know about the state of play comes from unnamed sources, some of them presumably speaking from inside the FBI with Mr. Comey’s approval. It would certainly be more useful to have such information on the record, from Mr. Comey, and with as much detail as possible. Can he offer clarification without further tipping the scales? There’s no way for us to know; all an outsider can say is: If he can, he should.

Whether he does or not, the way to cause no further harm is clear for the rest of us. It consists in large part of recalling what we already know: that Ms. Clinton, foolishly and arrogantly, ignored State Department guidelines and used a personal email server while working as secretary of state. That a thorough FBI investigation found no harm to national security in the practice, virtually no mishandling of classified information and no grounds for prosecution. That another device has come to the FBI’s attention that may or may not contain emails that may or may not have been sent by Ms. Clinton and may or may not be duplicates of emails the FBI already has examined. At this point, there is no reason to believe that new emails, if any, would be inconsistent with the story that has emerged. Nothing Mr. Comey said Friday changes that.

Meanwhile, here’s something else we know: Mr. Trump is the least qualified and most dangerous major-party nominee for president in our lifetimes. He is frighteningly cavalier about the use and spread of nuclear weapons; contemptuous of democratic norms and ignorant of the Constitution; totally unmoored from the truth in his public statements; unwilling to disclose the most basic information about his career and finances; disrespectful of women; and happy to base his campaign on division, racial hatred and religious prejudice.

Nothing Mr. Comey said Friday changes that, either.