Seeing quite a few scientists on twitter point out Biden's heightened risk of contracting on debate night given that the virus is airborne, it was an indoor/enclosed space, they were only standing several feet apart, and there was prolonged yelling between the two for almost 2h w/ no masks.

Plus a few ppl doing the math with respect to what a positive test *tonight* indicates, since its not like one is exposed and tests positive immediately - there's a lag. It's very likely 45 was contagious on debate night.