Undoubtedly, it’s a bullish sign for Biden to be this far ahead of Trump. In fact, since 1968, no incumbent president has trailed by as much as Trump heading into the first convention. However, before we get too carried away, the size of Biden’s pre-convention lead is unlikely to hold. After all, two other presidential contenders led by margins similar to Biden’s: Jimmy Carter in 1976 and George W. Bush in 2000, but by November their leads had all but evaporated. Carter only narrowly beat Gerald Ford by about 2 points nationally, while Bush won the most highly contested election in modern times, which took the U.S. Supreme Court to sort out.
Since 1968, the final national margin has differed from the pre-convention polling margin by an average of about 5 points. So if we were to apply that to the 2020 electoral environment, we’d be talking about only a 3-point national edge for Biden. That, of course, would increase the possibility that Trump could win the Electoral College even while losing the national popular vote.
One thing we’re watching closely as the GOP convention begins is just how much of a bounce Biden and Trump receive from the conventions. Given the unprecedented virtual convention format, it’s hard to know how much of a bounce Trump or Biden will receive, especially considering it’s gotten smaller in recent years and the conventions are scheduled back-to-back. And we’ve seen little change in Biden’s polling average — he’s averaged about 51 percent since last Sunday — and his lead has barely ticked up, going from 8 points to 9 points. For his part, Trump’s standing in the polls also hasn’t moved very much — he’s slid ever so slightly, from 43 percent to 42 percent — but of course, we haven’t gotten that many polls yet either.