Given the geometry of the venue, I think that would be the bullet after it had already struck President Trump.
SpyNavy
Garde la Foi, mes amis! Nous nous sommes les sauveurs de la République! Maintenant et Toujours!
(Keep the Faith, my friends! We are the saviors of the Republic! Now and Forever!)
LonePalm, le Républicain du verre cassé (The Broken Glass Republican)
yes that is the round already passed through his ear.
I believe this was a set up by the police and/or secret service.
Both the counter snipers were focused on that other roof. They where watching that shooter before he took the shot. Typically they're looking around.