I haven't read this whole thread, but I can't imagine the Secret Service would allow him too, POTUS or not. He's The President, not The King or God. He's essentially the top employee of the US Government, not above the law by any means.
In a shooting situation, the SS agents swarm all over the POTUS, I seriously doubt they'd want him waving a piece around trying to get some of the bad guy too.
I actually met the guy that grabbed Reagan and threw him in the limo, then leaped in on top of him and broke his rib. Guy's name was Sully, he's working for a telecom manufacturer now and taught a class in our office. I looked up the shooting on YouTube, and sure enough, there he was.