James Comey. Photo: Justin Sullivan/Getty Images

Today’s startling announcement by FBI director James Comey that the agency is looking into new evidence about Hillary Clinton’s personal email server looks at first glance like the ultimate in October surprises: a reopening of the possibility, however slight, of a criminal indictment of the person well on her way to becoming the next president of the United States, coming out 11 days before the election.

It is important to note some technical distinctions about what Comey’s letter to the relevant congressional committee chairs does and does not say. It does say new evidence has come to light that the FBI feels obligated to review. It does not say the evidence has been deemed credible, much less that it would change Comey’s recommendations on the overall issue. And the FBI, of course, is not the entity that would decide to prosecute even in the extremely unlikely case some “smoking gun” was found.

The obvious problem here is one of timing. The odds of any FBI investigation, much less one of this potential gravity, being completed by November 8 are limited. Assuming the FBI prevents leaks of the content of the new evidence or its nature, and Comey refuses public comment, that means the import of this development is one of those things that will almost entirely depend on partisan optics. Democrats tend to think the whole email saga is a huge nothing-burger, no matter what Clinton might have done to evade responsibility for it, and they’re not going to change their minds about that just because more emails have been thrown into the hopper. On the other hand, a previously sinking Trump campaign that has already loudly and repeatedly and redundantly asserted that Clinton is a criminal if not a traitor will obviously fan every suspicion available to keep open the door we thought the FBI had definitively closed.

There is no obvious precedent for anything quite like this on the eve of a presidential election. The midterm election of 1998 was held in the shadow of likely impeachment proceedings against Hillary Clinton’s husband; despite an apparent rebuke from voters, congressional Republicans barreled ahead with those proceedings as soon as they could. If nothing else, and assuming Republicans hang on to control of the House, the odds of a second Clinton impeachment just went up.

Donald Trump’s immediate reaction was not a very good sign this development will be received calmly. Addressing supporters in New Hampshire Friday, he hailed the FBI’s announcement — saying he had “great respect” for the agency’s decision to “right the horrible mistake that they made.”

“Perhaps, finally, justice will be done,” he said, as the crowd pumped fists and cheered. “Lock her up! Lock her up!”

That the emails the FBI is looking at reportedly arose from a separate investigation into Anthony Weiner for allegedly sexting with an underage girl, and were found on an electronic device that Weiner shared with Huma Abedin, his estranged wife, makes the whole situation all the weirder.

Clinton campaign chairman John Podesta has put out an angry statement demanding that Comey disclose what this is all about as soon as possible. But the one thing we know for sure is that this incident has blown up the old political maxim that inconvenient news can be buried by sneaking it out the door on a Friday afternoon.