I view this something like taking a poll of OSU and UM fans after a game. The losing side may dislike their coach more, or the QB, whatever, but they will still say their team is their favorite, almost no one will switch sides.
Similarly, I think about 40% of the electorate will ALWAYS vote D or R (at times they may not show up in numbers), and only ~20% is open to switching sides.
This is why a President's approval ratings will rarely drop much below about 40. That's the core, the convinced, the fan base, the partisans (which has a different meaning in another context).
So, turn out can be key, voters may be disaffected with their coach, and then the middle 20, who may not like either "team" very much, but will hold their noses at times and vote for one or the other.
The interesting thing, to me, is Trump clearly has about 30% locked up (he could shoot someone in NYC etc.). If he could appear to "moderate his tone" (stop laughing), he'd likely sway some of the 20, suburban housewives etc., and waltzing to a W. You don't need to be crazy any more.
I'm about 50-50 on whether Biden stays in the race. There is a lot of pressure obviously outside the inner circle, Joe may not feel any of it. And the recent polls show only a modest shift, so "they" may think they can wait this out.
