Election Update: The Swing States Are Tightening, Too

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In the more poll-obsessed corners of the internet, we’ve been arguing about Hillary Clinton’s decline in the polls against Donald Trump. Everyone seems to agree that Clinton’s lead is down quite a bit in national polls, to an average of around 3 percentage points from a peak of about 8 points shortly after the Democratic convention. But there’s a debate about how this translates to the state level.

My position is that a decline in Clinton’s national polls necessarily means that she’s declined in the states. There’s just no way around this; as we learned on Schoolhouse Rock, the United States is composed of 50 states and the District of Columbia. Perhaps it’s possible Clinton’s declined more in noncompetitive states than competitive ones — for instance, if Trump’s gains have mostly come from Republicans, widening his margins in red states but less in purple states. But that sort of conclusion is usually wishful thinking.¹

Still, there’s no better way to prove or disprove this than to look at polls of swing states directly. We’ve gotten a lot more of those polls recently, and they show pretty much just what the national polls do: Clinton’s lead in the states most likely to tip the balance of the election is somewhere around 3 percentage points.

Take the set of polls that Quinnipiac University released on Thursday afternoon. In the versions of the polls that include third-party candidates, Clinton led Trump by 5 percentage points in Pennsylvania and 4 points in North Carolina, but was tied with him in Florida and trailed him by 4 points in Ohio. The North Carolina result is slightly better for Clinton than our model expected, and the Ohio result was slightly worse — but overall, these results are consistent with the model’s hypothesis of a 3- or 4-percentage point national lead for Clinton.²

Quinnipiac’s aren’t the only polls out there, of course. The table below contains a simple average³ of recent polls in what we call “states to watch” — the set of 14 states that are most important to the national outcome. The average includes all polls in each state with a median field date of Aug. 21 or later — that is, polls conducted over the past two or three weeks. In some states, such as Nevada, the only polls that qualify by this definition are the 50-state online polls from Ipsos and SurveyMonkey, but in most others, such as Pennsylvania and North Carolina, there’s quite a lot of data to work with.

I’ve highlighted Michigan in the table because it would be the tipping-point state if the recent polls are right — that is, the state that would get Clinton to 270 electoral votes if she wins it along with all the states above it. She leads in Michigan by 3 percentage points in the simple average of recent polls, almost exactly matching her lead in national polls. That’s further confirmation that national polls and state polls tell pretty much the same story.

It’s interesting that Michigan shapes up as the tipping-point state in this analysis, since it’s one that had been considered relatively safe for Clinton before. But Clinton’s decline has been steeper recently in the Midwest, including in Michigan, Wisconsin, Ohio and Iowa. Conversely, her numbers have held up a little better elsewhere, such as in New Hampshire and Pennsylvania. That’s not to say there’s been no decline in these states, however. Recent Pennsylvania polls have had Clinton ahead by an average of 5 or 6 percentage points, which is nothing to complain about, but is down from the roughly 9-point lead she held in the state in mid-August.

Clinton’s Florida and North Carolina numbers have also held up comparatively well (although there’s a lot of disagreement among pollsters in both states). As a result, they’ve moved slightly closer to the tipping point and have become more important for Clinton, serving as a potential hedge for her in the event of a further deterioration of her numbers in the Midwest. On the flip side, some states presumed to be safe for Clinton might not be. Her lead in Colorado has fallen quite a bit, for instance, although this is somewhat counteracted by stronger polls in Nevada.

Some of these results look a bit different if you use the FiveThirtyEight model’s fancy-schmancy averaging methods, instead of the simple one I used above. For example, our adjusted polling average in Iowa has Clinton down 1 percentage point there, instead of 2 or 3 points. But the results don’t look that much different. Either way, Clinton is up by 3 points, give or take, in the states that matter the most.

Overall, Clinton’s chances of winning the Electoral College are 70 percent, according to our polls-only forecast, and 68 percent according to polls-plus. That’s a slight improvement in both cases from Wednesday, when her numbers were 67 percent and 66 percent, respectively.

FiveThirtyEight: Election forecast update – Sept. 8, 2016