My serious answer is that "Trumpism" will evolve and morph into a winning strategy for the GOP. Hardcore "populists" (i.e., those who specifically support Trump because of some perceived "populism" he embodies) will maintain that Trump permanently changed a "Romney GOP," and we are now seeing the evidence. Less populist conservatives will point to Trump's likely-less-volatile-and-more-intellectually-impressive successor as a "return to the norm."
What it will actually be is what has been happening since Abraham Lincoln - when the GOP loses an election (as I predict they will in 2020), they will reevaluate where the votes are. Richard Nixon clearly targeted Southern voters, for example, but he did it wisely; he did not alienate his Northern suburban base, and he famously remarked in his memoirs that he knew he'd never reach "the Wallace voter," and that this person wasn't his target (not saying he didn't win any Wallace voters, but that wasn't the strategy). Provided Trump loses in 2020, and the GOP is challenging Biden (or more likely his handpicked replacement) in 2024, I think the Republican nominee will try to "have it both ways." He will try to maintain gains among "White Working Class" voters, but he will also see the need to rebound in suburban areas a bit and get some outreach going to minority and younger voters.
Thus, I think you will see a "populist" GOP in the sense that the party knows its economic policies must have broader appeal than to the donor base. However, I think you will see less "culturally populist" appeals, hoping those people are already in the bag and feeling the current need is to reach out to perceivingly "flimsy" Democratic voters (i.e., people who might have voted for Romney). In other words, I predict an opposite of Karl Rove's 2004 strategy of targeting rural voters since he viewed the suburban areas as so rock solid that they didn't need to cater to them.
Which is why I wouldn't be surprised at all of a Nikki Haley nomination. She ticks a lot of those boxes and represents sort of a Nixon to the Goldwater movement before eventually a Reagan that fully realizes Trumpism (we have got to get a better term for this). The party isn't ready though to fully embrace it (and we've seen that with how trump has governed, passing tax cuts but not paid leave or lower drug costs) so a triangulation choice through someone like Haley is possibly needed. Although going all in with Josh Hawley is an option, it would be a much riskier proposition, much like running Reagan in 1968 over the safer Nixon.
