The Nate Silver article is a beautiful textbook example of the “post hoc ergo propter hoc” logical fallacy.
Before even showing that though there is the question of whether her so-called “dramatic fall” in the polls in the week or two before the election is actually a real fact or not. It was only a 3 point fall. That is not so much larger than the 2 point margin of error often cited. Given that the actual election fell outside his margin of error, perhaps the main lesson is margins of error were systematically understated and that it is quite possible much of the back and forth movement was due to sampling error and not a real change in the sentiment of the voters.
But assuming Hillary’s decline in the last two weeks was real, what evidence do we have that it was caused by the Comey statement? Yes it came first, but so did the Cubs making it into the World Series. Also the days were getting shorter, and leaves were falling in Wisconsin before her poll numbers dipped. Perhaps the Obamacare premium increases that came out in October that were the cause of her swoon. Yep, anything that happened before that can be singled out as the cause. That’s the logical fallacy.
Also why assume the net effect of Comey’s letter was negative. As Silver notes, the NYT did a big full court press on this story, but since it is only a slight exaggeration to claim no Trump voter in Wisconsin or Michigan read the NYT, it is at least as likely that the media coverage of the Comey letter shook some of Hillary’s base out of complacency and got them to the polls. Overall it helped her. At least I could make that argument and no one can prove me wrong.
Until there is data where an actual voter says “I switched my vote to Trump” and “The Comey announcement in October led me to make the switch”, the whole exercise is a debate bereft of any possible definitive resolution.
What is clear is that beforehand, Hillary (and much of the MSM ) did not think the Comey letter would have any decisive impact. Otherwise she would have scheduled some last minute campaign stops in Wisconsin and Michigan.