FiveThirtyEight: How Big Is Hillary Clinton’s Lead?

Here’s what we know: Hillary Clinton is leading in the race for president, and she’s made meaningful gains since last week’s presidential debate. Clinton is currently a 72 percent favorite in our polls-only forecast, up from 55 percent just before the debate. That corresponds to a roughly 4-percentage-point national lead for Clinton, about where the race was as of Labor Day — before a series of mishaps for her in mid-September. Our polls-plus model, which blends polls with an economic index and generally produces a more conservative forecast, has Clinton with a 69 percent chance instead. [...]

This makes for a pretty darned clear difference. In the set of pre-debate polls, Clinton was barely ahead. Out of 67 polls, she led in 34, trailed in 29 and was tied with Trump in four. That’s why our model had Trump drawing the Electoral College almost — but not quite — to a tie before the debate. We had a lot of data, much of it from high-quality pollsters. Clinton’s leads in potentially must-win states, such as Pennsylvania and Colorado, were tenuous. And she wasn’t clearly ahead anywhere else, although Florida and North Carolina were tossups. It wasn’t quite enough to make Clinton an underdog, but it was getting close. [...]

Speaking of trend lines, I’d remind you to be careful when examining them. Our model’s hypothesis is that Clinton has gained 2 to 3 percentage points since just before the debate, possibly with some upside on top of that based on events since the debate. Coming late in a close race, those 2 or 3 points are enough to improve Clinton’s odds quite a bit. (Think of an NBA team that sinks a clutch basket to go from a 2-point lead to a 4-point lead late in the game; its win probability improves a lot.) But Clinton’s post-debate gains are also not on the order of her convention bounce, which was something like 8 points instead — large enough to show up in almost every poll. Thus, you can find some polls where Clinton has gained as many as 7 points since the debate, but others where she hasn’t moved up at all — and even one or two where she’s lost ground. All of this is pretty normal.

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