The talking heads on CNBC's Closing Bell all indicated what has surfaced must be very serious for the FBI to reopen this investigation just 11 days before the election. I agree seriousness is likely, but will add another possible motive none of them mentioned.
Realizing the Bureau's public image has taken a huge hit, perhaps Director Comey reopened the investigation to try to salvage his, and the Bureau's reputation. He can safely do so now when the investigation's findings will arrive too late to influence the election.
I want to believe "reputation salvage" was not the FBI's main motivation. However, we've seen too much slipperiness in recent years not to raise the issue.
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Later ... The New York Times reports it was an investigation into Anthony Weiner's sexting of a NC teen that turned up the previously unseen Clinton emails on a computer jointly owned and used by Weiner and Abedin.
You see what draws Hillary and Huma together, both have sexual predator husbands. Meh, too many Democrats are low-life scum.