 Biden aides are skeptical of that claim. They think that Trump, who has been largely out of sight for the past four days, is spending more time on PrEP than he's letting on. Interestingly, Nora, a full 25 percent of voters in our poll said they're going to be tuning into the debate first and foremost to see if these two men have the mental and cognitive capacity to serve over the next four years.