This strategy was ultimately a policy failure, and it left Obamacare an established fact. At which point the G.O.P. was boarded and seized by candidate Trump, who clearly grasped the political logic of reconciling his party to some form of coverage expansion, even though he lacked an interest in actually hammering out the details. His campaign thus pointed ahead to a likely future in which the G.O.P. accepts a health care subsidy for the working class, without addressing all the internal reasons that the party can’t agree on what that subsidy should look like.

Those internal tensions that have given us the botch that is the House G.O.P.’s Obamacare alternative. It’s a piece of legislation caught betwixt and between: It includes enough in the way of tax credits and regulation to be labeled “Obamacare lite” by the party’s would-be ideological enforcers, but it also promises to throw many people off the insurance rolls — many Trump voters included — for the sake of uncertain policy goals. Its outline bears some resemblance to what the smartest conservative health policy thinkers favor, but it doesn’t want to spend the money (whether on risk pools or pre-funded health savings accounts or income-linked subsidies) that would make that approach politically viable. And its desire to spend less while keeping Obamacare’s most popular regulations (the ban on discrimination based on pre-existing conditions, above all) promises to make the risk of an insurance death spiral that much worse.

So it’s a bill that nobody on the right much likes: Not libertarians and not reformocons, not right-wing donors and not mushy moderates, not the Tea Party senators who promised full repeal and not the swing-state senators who well know that their own voters want the coverage expansion to endure. As for Americans who aren’t ideologically committed, forget about it: Passing the bill would be an invitation to a political beheading.

But in fairness to its designers, there was no bill that could have united all of the right’s disparate factions, because on health care policy, as on a range of issues, the Republican Party as an organism does not know what it believes in anymore.

Which brings us back to Trump’s resemblance to Jimmy Carter, who presided over a party suffering a similar crisis of belief. The political-science schema that makes the two men comparable figures is more compelling as history than as prophecy: It tells us how Trump could fail; it doesn’t tell us that he necessarily will. A strong-enough, savvy-enough, effective-enough president, placed in the transitional role that Carter occupied, could become transformative rather than disjunctive, and build a new ideological majority amid the rubble of the old.

And Trump does have a few of the necessary qualities. On policy he is incurious yet also more politically savvy than the party’s congressional leaders, more attuned to where his own voters and the country stands. His “workers party” is a more compelling vision for the right’s future than either status quo bias or “tax cuts plus nothing” zeal. With focus, attention and the judicious use of the bully pulpit, he could potentially bigfoot all the right’s ideological factions. Instead of tepidly embracing legislation that doesn’t come close to fulfilling his campaign promises, he could force his party to accept a bill that makes more political sense — be it the more redistributive plan advanced by conservatives like Avik Roy, or the federalist compromise floated by Republican Senators Bill Cassidy and Susan Collins.

Alas, as anyone on Twitter is regularly reminded, focus, attention and judiciousness are all qualities that this disjunctive president lacks. Which is why, even though nothing is inevitable, the Carter precedent — a majority wasted and then lost — looms as this administration’s most likely destination.