 They'll have to focus on Harris. Publicly, the campaign says that they're not worried, that it's the same issues and the same policies. But it's really not that simple. I mean, they're not the same person. They have different strengths and weaknesses. The Trump campaign has spent a lot of resources targeting Biden's mental acuity. And that attack line just isn't going to work against Harris in the same way, who is nearly two decades younger than Trump. NPR's Franco Ordonez reporting.