From “What do the polls say about a Harris vs. Trump matchup?” by Geoffrey Skelley and G. Elliot Morris at 538, via abcnews.com:
“While Harris consistently polled worse than Biden did against Trump before the debate, since then she’s sometimes polled ahead of Biden. In fact, Harris fared the same as or better than Biden in close to half of the post-debate polls: A near-bell curvedistribution in the differences between their margins in these polls is centered close to 0, suggesting little to no meaningful difference between how Harris and Biden performed.”
“And it seems that Harris’s stronger showing in these later polls is more about her having made up distance on Trump than Biden losing ground. Across nine national surveys before the debate, Harris did about 3 points worse than Biden on average, but in 25 post-debate polls, she’s only performed about 1 point worse than Biden on average — even as Biden’s margin in the same set of post-debate surveys also got slightly better.* Harris also improved her showing across the swing states, based on a very limited sampling of polls.
“To be clear, this doesn’t mean that Harris will run notably stronger than Biden, only that she could. Her post-debate polls against Trump relative to Biden have a great deal of variance, ranging from around 8 points worse to 4 points better than how Biden performed. Based on an average of 26 national polls conducted over the past month, Harris trailed Trump by 4.5 points nationally compared with a smaller 3-point deficit for Biden.
“Polling at the state level is limited at this point, with no more than four polls conducted in the past month in any battleground state. But based on the state-level polls we do have, things don’t look any more rosy for Harris there, as she lags behind Biden’s margin against Trump in the key battleground states for which we have data. In our aggregate of this limited set of polls, Harris trailed Trump by around 3 points in Wisconsin (Biden trailed by about 2 points), by almost 5 in Pennsylvania (Biden was down around 4) and by 5 in Michigan (Biden was behind by about 2). This raises the possibility that she could have a harder time than Biden winning the Electoral College and thus the election.
“Still, if Harris does end up as her party’s nominee, Democrats will hope that her polling improves as she mounts an active campaign against Trump. For one thing, Harris could experience something of a quasi-convention bounce in the wake of the coverage of Biden’s departure and her now-active candidacy. Moreover, until Sunday, any poll that tested Harris (or any other possible Democratic candidate) had been hypothetical for survey respondents. That is not the case anymore, which could at least partially reset the race and shift how some voters are thinking about it moving forward. For Democrats, Harris could represent an escape hatch from the doom spiral of negative media coverage that had hounded Biden following the June debate, as well as the heightened concerns about his capacity to serve at 81 years old and fears that he could not recover the momentum against Trump.
Skelley and Morris conclude: “If nominated, Harris could absolutely end up losing to Trump — after all, the same post-debate polling that suggested she could do better than Biden also pointed to a potentially lower floor of support. But for Democrats who felt like they were slouching toward defeat in November behind a candidate whom voters were increasingly unenthused by, a Biden alternative could shake up the race, excite the party and give Democrats a chance of rebuilding an anti-Trump coalition that could win.”
