OK, let's talk this out.
The GOP presidential primary is a likely going to be a crowded affair because Trump looks weak.
a) Trump is able to replicate 2016 by getting a plurality, but not a majority, of the delegates and wins like 2016 with weaker candidates dropping out along the way. Trump then gets badly beaten by Biden. ~20 points. And drags down the whole GOP ticket as the Democrats run across the country against the Fat Orange Bloviator, who is likely in serious legal trouble by this point.
b) Trump loses and tells all of his followers that the primary was rigged and 'the most corrupt evAR' and that they should stay home. This likely results in a GOP turnout drop of between %20-30 across the board in most elections.