Where is Kamala Harris’s convention bounce?
National conventions are among the biggest spectacles of the presidential campaign. What was once a formal exercise to adopt a policy platform and nominate candidates is now a political variety show. Tightly choreographed, each party performs an all-singing, all-dancing televised audition to the nation, culminating in a curtain call and balloon drop. While this might look out of place in an era of political cynicism, millions of voters watch and reward the garish performances in opinion polls. After Bill Clinton, then governor of Arkansas, took to the stage in 1992, for example, voters were so impressed that his poll numbers leapt eight percentage points, putting him on course for victory.
For many years the polling uptick seemed almost as choreographed as the convention itself, appearing on cue each election cycle. So much so, some election forecasters have formally incorporated the phenomenon into their statistical models. But with the conventions behind us, Democratic nominee Kamala Harris’s polling bounce is a no-show.
Empirically, convention bounces have been waning for some time (see chart). Before 2000 the spike was worth an average of 3.7 percentage points in two-party polling. Since then the post-performance high has been smaller—around 1.7 points—and has faded faster. But the absence of a jump in this year’s polls is still striking: Ms Harris’s post-convention gains are smaller than those of 17 of the past 19 Democratic nominees.
In some ways, the idea of convention bounces is rooted in an outdated version of politics. When more Americans consumed news through traditional media, especially television, conventions offered an opportunity to speak directly to them. Candidates were introduced on their own terms and delivered their message without journalistic interpretation. Conventions generated a stream of positive coverage. Convention poll boosts were therefore a combination of genuine persuasion (good vibes) and non-response bias (when partisans are more or less likely to respond to pollsters depending on the news cycle).
This effect may be diminishing. In 1992 when Mr Clinton accepted the nomination, around 22% of households tuned in, according to Nielsen, a media-research firm. This year the number was closer to 15%. Those who watched were more likely to be watching a partisan network. And polarisation means fewer voters are truly persuadable.
Ms Harris had her bounce before the convention even began. In the weeks following President Joe Biden’s withdrawal from the election, she had all but uninterrupted positive coverage, comparable to the convention buzz. She had a flawless roll-out, reintroducing herself and auditioning to be president. And despite being an incumbent vice-president, she seemed like a newcomer. In turn, she gained two percentage points in polls, putting her 4.7 points ahead of the final polls of Mr Biden’s campaign.
When it comes to forecasting the election, this is a conundrum. The Economist gives her a 52% chance of winning—effectively a coin toss. Our model does not include a formal convention effect, meaning it does not penalise Ms Harris for the absence of a poll bounce, as some other forecasts do. Given the dynamics laid out above, we think this is justified.
But although she has not had the convention uplift, the Democratic nominee may still experience the post-convention descent. Positive news coverage will not last forever and, unlike her opponent, there are few scandals and blunders already priced into her polling. With the election too close to call in these favourable conditions, it could be a matter of time before Ms Harris sees her own balloon drop.■
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