WASHINGTON — Why did he do it? FBI director James Comey spent 14 minutes laying out an unassailable case for prosecuting Hillary Clinton for the mishandling of classified material. Then at literally the last minute, he recommended against prosecution.

This is baffling. Under the statute (18 U.S.C. section 793(f)), it’s a felony to mishandle classified information either intentionally or “through gross negligence.” The evidence, as outlined by Comey, is overwhelming.

Clinton either sent or received 110 emails in 52 chains containing material that was classified at the time. Eight of these chains contained information that was top secret. A few of the classified emails were so marked, contrary to Clinton’s assertion that there were none.

These were stored on a home server that was even less secure than a normal Gmail account. Her communications were quite possibly compromised by hostile powers, thus jeopardizing American national security.

“An unclassified system was no place for that conversation,” said Comey of the classified emails. A rather kind euphemism, using the passive voice. In plainer, more direct language: It is imprudent, improper and indeed illegal to be conducting such business on an unsecured private server.

Comey summed up Clinton’s behavior as “extremely careless.” How is that not gross negligence?

Yet Comey let her off the hook, citing lack of intent. But negligence doesn’t require intent. Compromising national secrets is such a grave offense that it requires either intent or negligence.

Lack of intent is, therefore, no defense. But one can question that claim as well. Yes, it is safe to assume that there was no malicious intent to injure the nation. But Clinton clearly intended to set up an unsecured private server. She clearly intended to send those classified emails. She clearly received warnings from her own department about the dangers of using a private email account.

She meant to do what she did. And she did it. Intentionally.

That’s two grounds for prosecution, one requiring no intent whatsoever. Yet Comey claims that no reasonable prosecutor would bring such a case. Nor has one ever been brought.

Not so. Just last year, the Justice Department successfully prosecuted naval reservist Bryan Nishimura, who improperly downloaded classified material to his personal, unclassified electronic devices.

The government admitted that there was no evidence that Nishimura intended to distribute the material to others. Nonetheless, he was sentenced to two years of probation, fined and forever prohibited from seeking a security clearance, which effectively kills any chance of working in national security.

So why not Hillary Clinton? The usual answer is that the Clintons are treated by a different standard. Only little people pay. They are too well connected, too well protected to be treated like everybody else.

Alternatively, the explanation lies with Comey: He gave in to implicit political pressure, the desire to please those in power.

Certainly plausible, but given Comey’s reputation for probity and given that he holds a 10-year appointment, I’d suggest a third line of reasoning.

When Chief Justice John Roberts used a tortured, logic-defying argument to uphold Obamacare, he was subjected to similar accusations of bad faith. My view was that, as guardian of the Supreme Court’s public standing, he thought the issue too momentous — and the implications for the country too large — to hinge on a decision of the court. Especially after Bush v. Gore, Roberts wanted to keep the court from overturning the political branches on so monumental a piece of social legislation.

I would suggest that Comey’s thinking, whether conscious or not, was similar: He did not want the FBI director to end up as the arbiter of the 2016 presidential election. If Clinton were not a presumptive presidential nominee but simply a retired secretary of state, he might well have made a different recommendation.

Prosecuting under current circumstances would have upended and redirected an already year-long presidential selection process. In my view, Comey didn’t want to be remembered as the man who irreversibly altered the course of American political history.

And with no guarantee that the prosecution would succeed, moreover. Imagine that scenario: You knock out of the race the most likely next president — and she ultimately gets acquitted! Imagine how Comey goes down in history under those circumstances.

I admit I’m giving Comey the benefit of the doubt. But the best way I can reconcile his reputation for integrity with the grating illogic of his Clinton decision is by presuming that he didn’t want to make history.

I don’t endorse his decision. (Nor did I Roberts’.) But I think I understand it.

Charles Krauthammer’s email address is letters@charleskrauthammer.com.

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