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."
Trump will be exposed as the political disgrace that he is. Republicans will be running away from him as fast as they can. They may even change their method of nominating someone for President so that winner-take-all does not stick them with someone who get less than 30% in a six-way race in a critical state for the nomination.
The Republican Party still lists sharply to the Right, serving what are best described as mirror-image Marxists, people who believe that no human suffering can ever be excessive so long as it serves the Power, Indulgence, and Greed (get it-- PIG) of economic elites. I expect the Republicans to nominate someone of undeniable right-wing authoritarian values on economics and foreign policy while amenable to the sensibilities of the fundamentalist-evangelical wing of American Christianity.
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.
Republicans will need to open to people whose affiliation to the Democratic Party is shaky: what used to be the "Eisenhower" or "Rockefeller" Republicans who were solidly with the GOP through the Reagan era but were incompatible with the racist, anti-intellectual, demagogue-supporting types that came to the GOP through Nixon's "Southern Strategy". Those "Eisenhower" and "Rockefeller" Republicans recognize that their well-being relies heavily upon formal education and that they have much in common with the black bourgeoisie, middle-class Hispanics, and practically all Asian-Americans. These people are conservative in style, as one would expect of people with much formal education, and they have little tolerance for irrationality.
Note well that in 2008 Obama did extremely well with well-educated voters. So did Eisenhower. Obama support was positively correlated with formal education and income, which is usually how Republicans win. Electoral overlays for Obama and Eisenhower show Eisenhower winning much the same states, and the match between Obama and any other President in the last century is closer to those of Eisenhower than to anyone else. Political cultures have changed little in most states unless as demographic change, so figure that Massachusetts, Minnesota, and Rhode Island (usually tough states for a Republican to win) were much the same for Eisenhower, who won all three
twice as for Obama. (No I am not going to compare Adlai Stevenson to Donald Trump). Ike did worst in the Mountain and Deep South, also a weak area for Obama.
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.
The "low-information voters" for whom Donald Trump expressed love during the campaign know exactly what the economic agenda is from the GOP. Those people want politicians to punish what they alike see as exploiters and abusers -- like well-educated people such as the school teacher who corrects the grammar of their kids, intellectuals who ridicule young-earth creationism, wayward Hollywood actors, 'model minorities' seeming to have everything unfairly made in their favor, and in general people who recognize country music as deficient in intellectual appeal. Such people are incompatible with well-educated people in political life. The GOP cannot break up inter-ethnic coalitions that may involve people extremely different in culture (let us say Korean-Americans and Iranian-Americans).
Unlike some hard-core right-winger who pushes the Hard Right culture upon people to whom it is completely alien, Donald Trump let people believe that he was more mainstream. He may be a bigot, but he is no Bible-thumper. He denied science only at the behest of Corporate America which has its own agenda (Use more oil!), which is easy to get away with in a near-plutocracy. He has had two foreign-born wives, so he must be more cosmopolitan and intelligent than someone who takes pride in some all-American heritage. Trump seemed more mainstream than most GOP pols, so he might be less threatening than someone who would push fundamentalist Christianity as a solution to all problems. He had no record of votes in public office, so he could define himself.
Guess what -- Republicans will most likely end up with someone from a core area of the GOP -- the High Plains, Mormon Country, the Mountain South, or the Deep South. Republicans stand to lose a raft of Senate seats in states not rock-solid GOP in 2020... and it is not going to get better for them in 2022. (Here's looking at you, Pat Toomey!) The GOP must arrest its authoritarian-right death spiral so that it can connect to the political mainstream again.
