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Election Update: Even A Small Post-Debate Bounce Could Make A Big Difference For Clinton

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Like a lot of you, we at FiveThirtyEight are spending a lot of time refreshing our web browsers and Twitter feeds as we await new polls. Until we get more of those, figuring out how the first presidential debate affected the race involves a lot of guesswork. Still, the data that we have so far suggests that Hillary Clinton has gained ground as a result of Monday night’s debate — it’s mostly a question of how much her position has improved.

Four national polls have been conducted entirely since the debate: They have Clinton ahead of Donald Trump by 5 percentage points, 4 points, 3 points and 1 point. There’s also a new national tracking poll from the New Orleans Times-Picayune conducted mostly since the debate, and that has Clinton up 5 points. Considering that the 1-point lead was from Rasmussen Reports, which typically produces Republican-leaning results, the polls show a reasonably clear consensus so far of Clinton being up by 3 to 5 points nationally.

If that’s where the numbers wind up settling, that would reflect a meaningful bounce for Clinton, who was ahead by just 1 or 2 points nationally before the debate and in a tenuous position in key Electoral College states, such as Pennsylvania and Colorado.

The map starts to look a lot safer for Clinton if she’s up by 3 to 5 points instead. Take, for example, this post-debate round of battleground state polls from Public Policy Polling, which has Clinton up by 6 points in Pennsylvania, Colorado and Virginia, and up by 2 points in Florida and North Carolina. Those polls generated some oohing and ahhing on Twitter when they were published this morning, but they’re pretty much exactly what you’d expect to see in a race that Clinton leads by 4 points nationally, which is where PPP has the national race.

To generalize this a bit further, with a 3-to-5-point lead nationally for Clinton, we’d expect to see the following in the swing states:

  • A 4-to-8-point lead in Pennsylvania, New Hampshire, Colorado, Virginia, Wisconsin and Michigan, which have been slightly bluer than the national average this cycle.
  • Somewhere between a tie and a 4-point Clinton lead in Florida and North Carolina, which have been slightly redder than the national average.
  • A roughly tied race in Ohio and Iowa, which have been significantly redder than the national average.

I’m leaving aside a few states where there’s been a conflict between the polls and the demographics. In Nevada, for example, polls have been pretty good for Trump throughout this cycle, but it’s a hard state to poll, and I’m not sure how much I’d infer about the national race from how Nevada is moving. It also wouldn’t surprise me if some of the fringier swing states, such as Maine, Minnesota, Arizona and Georgia, move back in their usual partisan directions over the final weeks of the campaign. None of it matters much because with a 3-to-5-point lead, Clinton would have lots of ways to win in the Electoral College, and she could also tolerate underperforming her polls somewhat on Election Day. With a 1- or 2-point lead, by contrast, she’d have very little margin for error.

Of course, as I said at the outset, that 3-to-5-point range is just an educated guess based on the numbers we’ve seen so far and how past debates have moved the polls. Almost all the data we’ve gotten so far is from online polls and automated phone polls. Traditional telephone polls usually like to spend several days conducting interviews instead of turning polls around overnight. We should start to see some of those high-quality live-interviewer polls this weekend, and they may tell a different story than the quick-turnaround polls do.

Our forecast models could also take a few more days to catch up to whatever bounce Clinton has or doesn’t have. So far, she’s gained about 1 percentage point over Trump in the polls-only model, going from a 1.5-point lead in the projected popular vote before the debate to a 2.7-point lead now. Even that relatively small change has been enough to improve her chances of winning to 63 percent, up from 55 percent before the debate.

Clinton’s gains have been larger in the now-cast, a projection of what would happen in a hypothetical election held today. We’ve been de-emphasizing the now-cast because we find that people mistake it for an Election Day forecast, but it can be useful at times like these when you suspect some recent news event will affect the race and you want to see a projection that’s more aggressive about responding to that. Clinton currently has a 3.6-point lead over Trump in the now-cast.

FiveThirtyEight: Election Update – Sept. 30, 2016

Nate Silver founded and was the editor in chief of FiveThirtyEight.