And he deliberately choose the worst possible option. It took the FBI less than 48 hours to determine there was nothing new in those emails. Comey could have waited. He didn't.
I don't know nearly enough to attribute motive. And I don't think that the last-minute announcement had the impact that people claim. People who were stupid enough to think that the announcement was anything significant were the ones who were already stupid enough to vote for Trump.
Dan Quayle is all three