It’ll be interesting to see how he responds to this. I think an appropriate message would be something like, ‘This is terrible: assassinations only weaken democracy, and so no matter how great the threat Trump poses, his defeat must be electoral.’
To quote Dubya, I don’t think Biden “does nuance”. I doubt he’s equipped. Perhaps this big event will give him an excuse to exist the race and say it’s because of something other than the debate performance.