And on the one hand, Trump’s obsession with packing an arena makes some sense. Party conventions do traditionally boost a candidate’s standing in the polls. Since 1968, candidates’ vote share in national polls have increased, on average, by 5 percentage points after conventions. And considering Trump is currently at 41.5 percent in FiveThirtyEight’s national polling average — 9.6 points behind presumptive Democratic nominee Joe Biden — a boost in his numbers would be welcome news.
But on the other hand, there’s a real question of how much the convention bounce matters anymore. As you can see in the table above, convention bounces have been getting smaller, which is likely a byproduct of how polarized our politics have become. There are just fewer swing voters, so it’s harder for a candidate to attract support outside of his or her core base of supporters.1 That said, conventions can still matter, as once you get past the volatile post-convention period, one party tends to have a lasting lead in the national polls (though not necessarily the party whose candidate received the biggest post-convention bounce).
This year, though, there’s a real question about what kind of bounce a virtual convention will produce. Democrats worry that their mostly virtual event may be unable to replicate the energizing spectacle of a traditional convention. And although Trump is pushing for a large in-person convention, there’s no guarantee this will have the desired effect, either.