This is a very interesting thread, and brings up several questions to think about. One in particular that just came to mind is that, if you're being harassed by another driver, while on the road moving, and they brandish a weapon toward you, is that justifiable for a self defense case?
Mup, every case of deadly force will be judged on the elements of that specific case. I'm not an attorney and I don't pretend to know all the states laws on deadly force. But I have seen plenty of cases and have my own idea of what justifies the use of deadly force for me. "If a reasonable person would believe a person was in immediate danger of death or great bodily harm, the use of deadly force is justified."
"Reasonable person" is key it doesn't really mean what you believed; its means what a Judge or jury would believe they would have done in your circumstances..
"Immediate" means just that, and doesn't need a lot of explanation. The attacker stops what they are doing or moves away.
"Death" is obvious. "Great bodily harm" is not. Many people have tried to use the argument that someone threatening to punch them meets that requirement. Sometimes it works, sometimes it doesn't. I try my best not to get into a confrontation when armed. I'll take an azz whipping before I shoot someone punching me. Especially is I am a willing participant in and argument or incident.
I just watched "Accused: Guilty or Innocent?" Retired US veteran, Michael Ward, from Tennessee who had moved to Oklahoma shoots a wanted felon fugitive, on his property. They fought over a gun and the bad gun turned to run and Ward shot him in the back. I believe Ward feared for his life when he shot. However, "immediate" was gone. Ward will spend the rest of his life in prison.
You say "brandish". If you mean they display a weapon, that won't cut it. If they point a weapon at you or threaten you with a weapon, that's a different story.
My goal is twofold. Stay alive, and don't go to trial. Too often I see comments trying to justify the use of deadly force from someone saying they will kill anyone threatening their family as that is their duty. My duty to my family is to stay out of prison. And to not destroy our family financially with a trial.
Hope this helps.