But how big a subset?
How can we figure that one out? The extremists are redefining "Republican" in an ever-narrower and ever more extreme way...which means that the percentage of whackjobs and toxic partisans necessarily rises even while their numbers stay the same.
Do you call yourself a Republican only because it's the lesser evil? "Those Republicans" really don't suit you, judging by your often, dare I say it?, moderate positions. You're already a RINO, dude. They're pissing in your pool, too.