Still, if you look at our win-probability graphic, while Clinton’s chances were slightly declining already after she came off her post-debate peak, the rate of decline began to accelerate a couple of days after Comey, once we began to receive some post-Comey polls. Now the decline has leveled off, and her lead has held steady over the past several days. One advantage of having a model like ours that’s pretty quick to detect changes in the polls is that we can potentially make better inferences about the cause of polling shifts. And while it isn’t proof of anything, the pattern is at least consistent with a “shock” caused by a burst of negative news for a candidate, as opposed to a more gradual decline.
In fact, the shift looks pretty similar to a period in July after Comey reprimanded but did not charge Clinton for her email server and testified before Congress about it. That period produced about a 2-point swing against Clinton.
The news may also have had an effect down-ballot. Democrats’ chances of winning the Senate were generally hovering around 70 percent in late October. Today, they’re 50 percent.
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