Shots fired at Trump rally, page-890

Very good observations, and your evaluation of SS protocol is spot on
The last sentence is key if there was any doubt.

But where I agree with you is that they do appear to have their sights on something in the very near vacinity to where the shooter was located.Even potentially more disturbing is that they even appear to then disengage from their sights moments before the shots ring out. Before going back to their sights and then neutralizing the gunman with quick successive shots. Related to that they also don't appear to have to alter their site picture by rotating their rifles before firing, suggesting their sights were already on target.