Support for Trump was understandable in 2016 when it was unclear how he would actually behave in the Presidency. Most Republicans I know saw it as a faustian bargian: have a Republican wacko in the White House or a Democrat. But I really don't see this persisting in 2020. I would not be surprised if Republicans employ ranked choice voting for their primary, or increase the number of superdelegates or otherwise take steps to avoid one primary candidate succeeding through appealing to a minority of Republican primary voters. We're already seeing Republicans like Romney distinguishing himself through opposition to Trump.

Ultimately who knows - Trump might actually live up to his promise to run in 2024. But I am dubious that Trumpism will be anything but an aberration in the party. He managed to lose as an incumbent. That's a substantial failure, and one I think Republicans will remember.