Holman W. Jenkins Jr. recognizes that Donald Trump is a shrewdly calculating utilitarian who is in it for himself. What, he wonders, will happen if Trump decides at some point that he cannot win?

Before they gather in Cleveland for their convention, it’s not too soon for Republicans to begin thinking about what exactly a Donald Trump defeat might be like.

As with his now-documented habit of charitable promises that seldom materialize, Mr. Trump never intended to endanger a sizable part of his personal wealth to fund a presidential campaign. That means he’ll continue to campaign on the cheap, by saying incendiary things and having them transmitted by the free media. Expect more speeches like the protectionist-cum-conspiracy theory speeches in suburban Pittsburgh on Tuesday and New Hampshire on Thursday, even if such diatribes frighten major donors and mainstream Republicans and make life harder for down-ticket Republican candidates in the fall. …

Here resides the problem all along for those hoping for a Trump-to-the-middle move. Such moves are expensive. Base-broadening campaigns require lots of paid TV to reach non-engaged voters and Trump skeptics, pummeling them with reassuring images suggesting that a Trump presidency would be OK.

Mr. Trump not only is unwilling or unable to finance such a campaign. He evidently is unwilling to do what’s necessary to entice GOP donors to finance it on his behalf. This means GOP officeholders seeking re-election can expect a constant headwind of inflammatory Trump statements designed to stimulate the free media coverage that his asset-lite campaign requires. Republican candidates up and down the ballot therefore become unwilling sharers of a high-risk Trump electoral wager, a gamble more likely to end in a Hillary landslide than a Trump White House.

The more intriguing question concerns what happens if Mr. Trump decides he can’t win and no longer is willing to throw good money after bad. Unless they were born on a turnip truck yesterday, campaign vendors will be the first to figure it out. Look for them quickly to cut off services rather than get stiffed in the inevitable Trump campaign bankruptcy filing.

Mr. Trump’s harsher Republican critics are kidding themselves to think Mr. Trump is crazy or unstable and will suffer a breakdown. More likely, he will simply and coldbloodedly toss the ball to the GOP, saying, in effect, “If you want to pay for some events or TV, I’m available. Otherwise I’m done.” The GOP would then have to shoulder the dual burden of propping up a minimally respectable Trump campaign while also distancing its down-ballot candidates from Mr. Trump so they might survive.

And that’s the optimistic scenario. Mr. Trump has learned the value of audacity. He might well decide to cover his retreat and preserve his amour propre with a flurry of lawsuits and conspiracy theories about a “rigged” election.

He’s already begun putting narrative flesh on these bones. He speaks of “crooked Hillary” and increasingly of the Clinton Global Initiative, Bill Clinton’s philanthropy, and what he calls the Clintons’ “politics of personal profit and theft.” In his trade speeches, he portrays the Clintons as members of a nefarious global elite that has enriched itself while foisting impoverishing trade deals on the U.S. middle class.

He perhaps will throw in a few suggestions that foreign governments hold hidden leverage over Hillary because of her hacked, illegal email server. He’ll mention Bill Clinton’s pardon of Marc Rich.

Republicans can also expect to be a target of his accusations. He doesn’t need to be plausible, just tell a story that justifies his own stance that he didn’t lose, the other side cheated, “Washington elites” conspired against him, etc.

If the Trump endgame is destined to go this way, Republicans should hope it does so early, ideally before the convention is even over. To date, Mr. Trump continues to tease top GOPers and conservatives with the idea that he may yet come their way, turn his formidable talents to advancing conservative causes. This merciless exploiting of Republican romantics has begun to seem like something out of “The Blue Angel” or Lucy with the football.