When is the last time somebody got elected President without running as a D or an R - or even came close?
Like it or not, about half the voters are going to blindly vote along party lines, regardless of who the nominee is.
Quitting the Republican party means you give up those blind party voters, and throw the race to the Democrat.
There has been one man, in my lifetime, who could have pulled it off. Given that, it would have taken an extraordinary circumstance to give Trump the opportunity. That opportunity occurred when the entirety of the DC GOP went all in publicly on the coup 1/7. Had Trump denounced, who I denounced on 1/7, he could have taken the majority of his eighty plus million voters with him. Oh, but what a chance! Trump could have destroyed the GOP. The VERY SAME people who chased Trump out of town are still calling every shot. The Swamp = DC GOP. You are a fool is you think you can reform them. You must blow it up and start with a real second party.
Perot with 17%. He was better than Pop Bush by a mile.
He was also spot on about NAFTA and globalism.