The appetite among Republicans for repudiating President Donald Trump, defending democratic norms and deploring nativism, xenophobia and protectionism is apparently so slight that the only major Republican elected officials willing to go after him are two moderate female senators (Lisa Murkowski of Alaska and Susan Collins of Maine), two senators not seeking re-election (Jeff Flake and Bob Corker), Sen. John McCain, R-Ariz., and moderate Rep. Charlie Dent, R-Pa., who is also retiring.

Maybe a disaster for the GOP on tax reform or a blockbuster report from special counsel Robert Mueller will change more minds and stiffen more spines, but I sort of doubt it. So long as major Republican figures such as Sen. Tom Cotton (Ark.) enable Trump and cheer him on, so long as Breitbart and Fox Non-News spin disasters into political gold and so long as Republican House committee chairs disgrace themselves by opening investigations − of Hillary Clinton − one should not expect many more Jeff Flakes to step forward.

Donors, operatives, elected officials and activists within the GOP either have drunk the Trump Kool-Aid or lack the nerve to say what they know to be true. Unless something radically changes, the GOP does not look capable of ridding itself of Trump. And even if it did, look how Republicans have demolished the principles that were supposed to be the foundation of the party of Lincoln.

Clearly, there will be a gap in the political landscape going forward if the GOP remains under Trump's spell − a space that could be filled with a center-right or centrist party. That's the territory that Ohio Gov. John Kasich, R, Flake, Corker and others could stake out in 2020. If the Democrats, who have their own issues (more about that in a moment), follow Sen. Bernie Sanders, I-Vt., into political oblivion, there also will be some center-left voters looking for alternatives to the two parties.

As for center-left Democrats, their concern for their party's future is only slightly more muted than #NeverTrumpers' worries about the GOP. President Barack Obama's car czar, Steven Rattner, recently wrote that for Sanders, "the war is just beginning":

"Mr. Sanders − who, of course, isn't even a registered Democrat − is banging on about what he calls 'Medicare for All,' a government-run plan that would provide health care coverage for every American. . . A goodly number of those senators are presidential hopefuls, leaving their prospective campaigns open to attack from Republicans salivating to capitalize on an idea that has historically been a political graveyard. Remember Hillarycare?

"As a centrist Democrat, I'm scared to see my party pulled into positions that are both bad politics and dubious policy. And I'm disappointed that few of our party's moderates are willing to resist the freight train coming at us from the left. . . . Amid the many complications of Medicare for All, the question of what would happen to the 157 million Americans who get their insurance from their employers and the 19 million who are enrolled in Medicare Advantage loom large."

Instead, Rattner urges the Democrats to return to a tried-and-true message − " 'Better Jobs for All' − big ideas for addressing our most pressing economic challenge. That is: the wage stagnation that has left too many Americans behind, particularly white working-class men."

Gosh, this sounds familiar. A populist who cares little for the party (which he didn't identify with until he ran for president) throwing out unattainable, extreme ideas that moderates are too frightened to take on − and a party without a clear, compelling message. Take it from one who has seen this horror film once before − if Democrats do not provide a muscular response to a populist showboater, they'll see him abscond with their party.

If that occurs (and I certainly wish it does not, just as Democrats of good will should hope that Flake succeeds), we might effectively, if not literally, have four parties: the ethno-nationalist GOP, non-Trump Republicans, center-left Democrats and Sanders's democratic socialists. We are, one senses, on the cusp of something very new, if not unprecedented in a country heretofore wedded to a two-party system. What form that takes is anyone's guess. But Flake and other GOP refugees from a Trumpified GOP, I suspect, will have a role to play.

Jennifer Rubin writes the Right Turn blog for The Post, offering reported opinion from a conservative perspective.