Assessing Clinton’s Bounce in the Polls Following the First Presidential Debate

Last week, I wrote that it was still unclear how the first debate might affect the trajectory of the Presidential race.

Well, things became a bit clearer over the weekend and Monday after a slew of new poll results were released showing mostly good numbers for Clinton.

Clinton leads Trump in 46 out of the 71 polls released since the first Presidential debate on September 26. Meanwhile, Trump leads Clinton in only 23 of these polls (they’re tied in the remained two polls). Furthermore, according to my model, Clinton’s chances of winning in November are better today (October 4th) than they were the night of the debate. She currently has a 68% of becoming the 45th President of the United States, up from 63% on September 26.

Yet, Clinton hasn’t necessarily gained ground since the debate. Rather, it’s Trump who has lost support.

A look at national polls shows that Clinton’s support nationwide is essentially unchanged since before the debate. In polls conducted between September 19 and September 25 (a week before the debate), Clinton led Trump, on average, 47.75% to 45.25%. But in polls conducted since September 26, she now leads him, on average, 47.11% to 42.98%.

So since the debate, Clinton has lost about half a percentage point, whereas Trump has lost closer to 2.5 percentage points.

Clinton also appears to have made meaningful gains in a number of key battleground states since the debate – states such as Colorado, Florida, Nevada, North Carolina, and Pennsylvania.

The graphic below shows an estimate of the size of Clinton’s post-debate bounce in every state for which post-debate polls have so far been released (as of October 3). Importantly, the numbers in the graphic below do not reflect which candidate is currently in the lead in each state. Rather, the numbers reflect the difference between the post-debate spread and the pre-debate spread, with spread calculated as support for Clinton minus support for Trump.

Therefore, if Clinton led Trump in Pennsylvania by an average of 5 percentage points prior to the debate and she now leads him by an average of 7 percentage points, then this would constitute a 2 point bounce for Clinton in the Keystone State. Meanwhile, if Trump led Clinton in North Carolina by an average of 3 percentage points before to the debate and he now leads her by an average of only 1 percentage point, then this too would constitute a 2 point bounce for Clinton.

I emphasize that these numbers only represent rough estimates of how Clinton’s post-debate bounce in each state might look because, for most states (Colorado, Florida, Nevada, North Carolina, and Pennsylvania are exceptions), only one poll has so far been released since the debate. Therefore, for states with only one or a few post-debate polls, my estimates of Clinton’s bounce might be rather unstable or might merely reflect random deviation from the state average.


Yet if the estimates above are accurate, then Clinton may have made gains in 29 out of 41 states for which post-debate polls have so far been released (those colored in blue). And even though she may not be currently leading in each of these states, her well-received performance in the first debate might have helped her to narrow some gaps.

A potentially important accomplishment with only 35 days to go until Election Day.


Brian Kurilla is a psychological scientist with a Ph.D. in cognitive psychology. You can follow Brian on Twitter @briankurilla 

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