Republicans who think that "Trumpism" will just go away after Trump loses and that the Republicans will nominate another Bush-type Republican in 2020 are deluding themselves.
People who think Trumpism represents a coherent set of views that will survive past Donald Trump's candidacy rather than a segment of the population overjoyous that a candidate will publicly say all of the xenophobic and racist things they say behind close doors and cloak it as "straight talk" are deluded.
Of course they're deluded, but they have enough share of the Republican primary vote to push their candidate into the nomination. Why would that change in 4 years? It's not like they'll leave the party if Trump loses.
I think Donald Trump has a very, very unique appeal. As I've said in other posts, he had a slew of people supporting him for TOTALLY separate reasons; I'm highly skeptical that some carbon copy of him can achieve the same mass appeal. He was the populist to Fuzzy Bear, the no-political-correctness guy to Classic, the America-first non-interventionist to Sanchez, the nominee you have to support to Lincoln Republican and the non-politician who will stand up to the Democrats on budget battles because he's not part of the DC club to my dad. There isn't going to be another personality with that much name recognition in that great of a situation to run in 2020, IMO.
"Trumpism" shouldn't be used as a phrase for anything other than undying support for Donald Trump himself.
