What’s unusual is seeing these two strategies deployed with such force at the same time. Trump has done so little over the course of his 3½ years as president to broaden his appeal that he has little choice but to believe his base can once again thread the Electoral College needle. Biden defied conventional wisdom by talking as much as he did about bipartisanship while winning a partisan primary, so he has every reason to lean in even harder now. The result is a general election where both candidates are fighting over Republican and right-leaning independent voters.

That’s a battle Biden has been winning. Before the conventions, polls have generally found him performing a bit better among Republicans and conservatives than does Trump among Democrats and liberals. For example, in this month’s Fox News poll, in which Biden led Trump by seven percentage points overall, Biden got 8% of the Republican vote. That may not seem like much, but it’s double what Trump got of the Democratic vote. And Biden did even better among conservatives with 21%, while Trump got only 12% of the liberals.

We often assume Trump’s base is fervently loyal, while progressives remain tepid on Biden at best. However, tepid support beats lost support. Trump’s base has suffered demonstrable erosion. Biden’s base has not.