What the polls say after the first presidential debate

Unless you live under a rock, you probably heard about the debate between President Joe Biden and former President Donald Trump last Thursday. Biden's halting performance on the debate stage looks to have exacerbated voters' concerns about whether he has the mental and physical fitness to serve another term as president. Although Trump spent much of the debate repeatedly pushing falsehoods, viewers came away with a pretty concrete opinion that he'd won the debate — or, at the very least, that Biden had lost it.

It's still early, but Trump looks to have gained at least some ground in the polls as we begin to examine the immediate fallout from the debate. In 538's national polling average, Trump now leads by 1.4 percentage points over Biden, while the two candidates were just about tied on June 27, the day of the debate.

Much of the initial post-debate polling has shown Trump in a stronger position relative to where he was in the last pre-debate surveys from the same pollsters. For instance, Democratic-aligned pollster Data for Progress released a national survey conducted the day after the debate that found Trump ahead of Biden 48 percent to 45 percent, whereas an early May poll from the same outfit had Biden ahead 47 percent to 46 percent. In its post-debate survey, Suffolk University/USA Today found Trump leading 41 percent to 38 percent (with Robert Kennedy Jr. at 8 percent), a shift from a tied race in late April. Leger, a Canadian pollster, found an especially dramatic shift in its polling collaboration with the conservative New York Post, going from Biden +2 just before the debate to Trump +7 right afterwards.

That's not to say every poll found Trump gaining. Some other pollsters, such as SurveyUSA, also released post-debate numbers that had Trump ahead nationally, but don't have a relatively recent point of comparison (SurveyUSA last released a nationwide poll in February, in which Trump actually had a slightly larger lead). Morning Consult's national polling found the race essentially unchanged, with a pre-debate tracking survey showing the two candidates tied at 44 percent and the comparable post-debate tracker showing Trump up 44 percent to 43 percent. CNN/SSRS's new poll found Trump leading 49 percent to 43 percent in a head-to-head matchup, but those are the same numbers as the pollster found in late April. And we're still waiting for some other high-profile pollsters to give us their first post-debate snapshot of the race. In line with G. Elliott Morris's analysis of historical polling last week, we usually like to see about two weeks of data after a high-profile event to gauge just how much a race has shifted.

Nonetheless, some post-debate surveys offered other negative data points for Biden's standing with voters after the debate — including those in his own party. In the 538/Ipsos post-debate survey, conducted using Ipsos's KnowledgePanel, just 20 percent of likely voters, down from 27 percent before the debate, rated Biden's mental fitness to be president as excellent or good — that includes a drop from 56 percent to 42 percent specifically among Democrats. And just 15 percent of voters after the debate said his physical fitness to be president was excellent or good, down from 21 percent before the event. Similarly, a YouGov/CBS News post-debate poll found that only 27 percent of registered voters thought Biden had the mental and cognitive health to serve as president, compared with 50 percent overall who felt Trump did. Among Democrats, only about three-fifths thought Biden had the mental wherewithal to do the job.

Additionally, conversations about Biden potentially dropping out of the race have mushroomed in the media, and among Democrats concerned about his debate performance. It’s unclear if Biden might really step aside, but Texas Rep. Lloyd Doggett made headlines on Tuesday by becoming the first Democratic member of Congress to call on Biden to do so. Pollsters in this landscape have tested voters' views about some potential alternatives for the Democratic nomination. In its post-debate survey, Data for Progress polled eight other theoretical Democratic candidates against Trump, but found all of them polled pretty similarly to Biden. For instance, Vice President Kamala Harris, far and away the party's most likely replacement choice, polled identically to Biden. Conversely, CNN/SSRS found Harris trailing Trump by 2 points compared with Biden’s 6-point deficit. DfP, Morning Consult and SurveyUSA also asked Democrats who they'd prefer if Biden stepped aside, and Harris led each poll by varying margins.

For now, the initial post-debate poll movement hasn't notably shaken up 538's presidential election forecast, which still shows a coin-flip race between Biden and Trump. However, the forecast remains pretty conservative this far out from the election, so we wouldn't expect to see drastic swings based on small and inconsistent shifts in a handful of national polls. Still, should we see more movement in Trump's direction in state-level polls in the coming days, the forecast will likely start to tilt his way to some extent. (Later this month, Trump may also get a boost from a potential VP announcement and the Republican National Convention.)

But despite Biden's struggles, dramatic polling movement in the next couple of weeks would be a surprise. After all, the electorate is highly polarized, such that most voters considering one of the major-party contenders already lean toward one or the other candidate, and aren't particularly likely to jump ship. For instance, in the post-debate 538/Ipsos poll, the share of likely voters who said they were considering voting for Biden fell by about 1.5 points from before the event, while the share considering Trump grew by 0.4 points — but those changes were smaller than the survey's margin of error, and very few voters said they were considering both Biden and Trump. Somewhat similarly, 5 percent of debate watchers said the debate changed their minds about whom to vote for in CNN's flash poll right after the debate, too small a figure to readily know just how those shifts affected each candidate's support, such as whether it reflected voters going from undecided to one of the candidates.

Nevertheless, any movement in voters' preferences could matter a great deal to the final outcome in our current era of highly-competitive presidential elections. Over the past six presidential elections, just one (2008) had a national popular vote margin larger than 5 points. And of course, we decide presidential elections in the Electoral College, where the race can end up being even more competitive. For example, in 2020, Biden garnered a 4.5-point advantage nationally but won the "tipping-point" state of Wisconsin by just 0.6 points to clinch victory. That's another reason to keep a close eye on state-level polling as we move forward. Even a small shift toward Trump in some parts of the electorate, relative to four years ago, could easily set up a Republican return to the White House.