If you're just going to waive it around to scare them off, then you've screwed up.
Sticking around to argue with them was another mistake. He should have left.
I can only half agree with you. If the threat recedes when you present your gun, then you are no longer justified to shoot. You can only shoot when you have imminent threat of death or great bodily harm to you or someone else you are protecting. I would say that, in a sane world with sane DA's and prosecutors, the fact that he ultimately did not fire will be to his advantage. The question to bring charges will be answered by what his state of mind was at that moment and whether he was in fear for his life or serious bodily harm when he presented the firearm. I think the answer to that is yes.
There is another condition to be aware of. He needs to be 'clean', that is he cant have been an instigator himself. That may come down to why he was there in the first place. Which 'rally' was condoned by the city and which party just decided to show up and be disruptive (pro-Trump vs BLM/Antifa).
I will add one more thing that I advocate strongly for. That is if you carry, get a good protection benefit/insurance like US Lawshield. At least then you wont go broke defending yourself from the aftermath of what is otherwise a justied use of your firearm for defense.
If you’re feeling sufficiently threatened to warrant pulling the gun, then you’d better shoot the threat.
Tough call here. If he had started shooting they might have swarmed him with those shields and bats. Notice one Antifa trooper shattered his cab window with a pipe or bat. The driver appeared to have been tear gases as well while he was inspecting the damage. So he pulled while partially blinded.