Harris got a polling bounce before her convention, not after

The 2024 presidential race may go down in history as one of the most difficult elections to analyze thanks to its many twists and turns. One notable challenge will be measuring the much-ballyhooed "convention bounce," whereby candidates' support in the polls sometimes increases following their party's intensely-watched formal gathering. Normally, a look at how the polls have changed a week or two after each party convention could give us a sense of whether or not the event gave its party a boost.

But that's proving to be a lot trickier in 2024. Just think of the whirlwind — for once not a term of exaggeration — of political events in the past two months that we need to consider in how we read any changes in public opinion:

Goodness gracious, great balls of fire — that's been a lot for Americans to take in. Not only that, but the near-term overlap of many of these events has made it mostly impossible to isolate the effect that any one of them may have had on public opinion. For instance, any boost Trump enjoyed after the Republican convention may have also had to do with the attempt on his life two days before the convention or buzz generated by his selection of Vance as his running mate on the first day of the convention. Then, of course, Biden dropped out on July 21, meaning that polling of the race effectively reset like on an old Super Nintendo just three days after the Republican convention ended — and blowing in the cartridge won't necessarily make it easier to interpret the images on screen.

All this means that, while their situations clearly differ, Harris and Trump both have complicated stories when it comes to reading their post-convention position. Trump's share of the vote improved by a little over 1 point in the polls from the start of his convention through the day Biden dropped out. And while it's possible that trend may have continued had Biden stayed in the race, that campaign reset means we only had three days to directly gauge the polling impact of Trump's convention. Ultimately, Trump's standing in the polls has remained stagnant since then, and his small post-convention bump is now something of a historical footnote.

For her part, on paper, Harris didn't really get a bounce: At the start of the Democratic convention on Aug. 19, she was polling a tad shy of 47 percent in 538's national average, and a week after the convention ended, she's sitting just above 47 percent — a negligible change of around 0.5 points:

Harris's lack of a bounce fits in with the recent trend of smaller-to-insignificant improvement for nominees after their conventions. Overall, candidates since 1968 have averaged about a 2-point increase in their polling vote share from the start of their convention to a week after its conclusion. But while 11 of 16 candidates from 1968 to 1996 saw at least a 2-point post-convention bump, only 5 in 14 since then could say the same. A more polarized electorate is a primary culprit for this trend, as fewer voters are up for grabs now than in the past, even in cases when voters are still getting to know candidates who haven't long been on the national stage.

Yet the absence of a post-convention bounce for Harris doesn't mean she hasn't enjoyed a recent improvement in the polls. When 538 kicked off our polling average for the Harris-Trump matchup on July 24, Harris stood at about 45 percent, almost even with Trump's 44 percent. But by the time her convention kicked off on Aug. 19, Harris's standing had improved by roughly 2 percentage points to about 47 percent, while Trump's average continued to hover around 44 percent — which is around where both of them sit in our most recent polling average as well.

Harris's polling growth likely happened because her campaign experienced many of the conditions that typically accompany a national convention in the weeks before the actual party gathering. After all, the hullabaloo over Biden's withdrawal, Harris's candidacy and her selection of Minnesota Gov. Tim Walz as a running mate provided much of the same wall-to-wall coverage and energizing of the party base that a modern convention aims to generate. All these developments on the Democratic side of the ticket might additionally have diminished any burgeoning bounce that Trump may have been starting to see — creating a situation akin to holding the Democratic convention immediately after the GOP event instead of a month later. Considering the rampant attention paid to the campaign fireworks of late July and early August, it's not surprising Harris got a bounce ahead of her convention.

A big part of that story is the sizable shift in how Americans perceive Harris now that they are becoming more familiar with her as a political entity separate from her role as Biden's vice president. On July 21, 38 percent of Americans held a favorable view of Harris in 538's average, while 52 percent held an unfavorable view. But as of Aug. 30 at 2 p.m. Eastern, opinions of Harris were almost evenly split, with 46 percent holding a favorable view and 47 percent holding an unfavorable one. Similar to her standing in the polls, Harris's favorability average has only ticked up a tad — by about 1 percentage point — since the end of the Democratic convention, but she has seen an 8-point improvement in her favorability since Biden dropped out of the race.

Finally, this topsy-turvy race experienced another shock just one day after the Democratic convention that likely drew some attention away from Harris and could affect the polls: Independent candidate Robert F. Kennedy Jr. suspended his campaign and endorsed Trump on Aug. 23. How that will influence the choices of the approximately 5 percent of voters who said they planned to back Kennedy at the time remains to be seen.

However, 538's analysis of polls from before Kennedy's departure suggests that his exit probably won't matter that much. We found that Trump gained just 0.2 points in margin when shifting from a multi-candidate contest involving Kennedy to head-to-head race against Harris — a tiny amount that's about equivalent to the average absolute daily change in 538's polling average. Unlike in 1992, when independent Ross Perot's withdrawal on the final day of the Democrats' convention that July helped boost Bill Clinton, Kennedy had far less support in the polls at the time of his exit, reducing his departure's potential impact on post-convention polls. (And while Kennedy left the door ajar for people to vote for him this November, he is extremely unlikely to pull off the same feat as Perot by formally reentering the race in early October and winning 19 percent of the national popular vote!)

In a summer that's seen an unparalleled series of campaign events, the Democratic convention proved more typical in its negligible impact on the polls. However, that's in part because Harris's entry had already altered the race so dramatically beforehand. Heading into Labor Day, the traditional start of the stretch run of the campaign, Harris maintains a slight edge over Trump — though we're sure this campaign will see many twists and turns still ahead.