Here is my theory after thinking a long time about this:

What if Trump had his own sniper that day and this is the person who actually took out the assassin or possible assassins? If that were the case, it would explain why he was grazed in the ear. He did get lucky by turning his head and they really did almost kill him. That part wasn't staged for dramatic effect. However, Trump having a sniper who wasn't tied to the deep state Secret Service would give Trump a puncher's chance.

If such a sniper were there that day, he may have not had access to Secret service radio comms, and would thus need to spot the shooter(s) himself. It would explain why the shooter(s) were able to get shots off, with one grazing Trump. Maybe this was the dark figure on the water tower.