One important answer would be to spend a bit more money. Obamacare has turned out to be remarkably cheap; the Congressional Budget Office now projects its cost to be about a third lower than it originally expected, around 0.7 percent of G.D.P. In fact, it’s probably too cheap. A report from the nonpartisan Urban Institute argues that the A.C.A. is “essentially underfunded,” and would work much better — in particular, it could offer policies with much lower deductibles — if it provided somewhat more generous subsidies. The report’s recommendations would cost around 0.2 percent of G.D.P.; or to put it another way, would be around half as expensive as the tax cuts for the wealthy Republicans just tried and failed to ram through as part of Trumpcare.

What about the problem of inadequate insurance industry competition? Better subsidies would help enrollments, which in turn would probably bring in more insurers. But just in case, why not revive the idea of a public option — insurance sold directly by the government, for those who choose it? At the very least, there ought to be public plans available in areas no private insurer wants to serve.

There are other more technical things we should do too, like extending reinsurance: compensation for insurers whose risk pool turned out worse than expected. Some analysts also argue that there would be big gains from moving “off-exchange” plans onto the government-administered marketplaces.

So if Mr. Trump really wanted to honor his campaign promises about improving health coverage, if he were willing to face up to the reality that Obamacare is here to stay, there’s a lot he could do, through incremental changes, to make it work better. And he would get plenty of cooperation from Democrats along the way.

Needless to say, I don’t expect to see that happen. Improving Obamacare requires doing more, not less, moving left, not right. That’s not what Republicans want to hear.

And the tweeter-in-chief’s initial reaction to health care humiliation was, predictably, vindictive. He blamed Democrats, whom he never consulted, for Trumpcare’s political failure, predicted that “ObamaCare will explode,” and that when it does Democrats will “own it.” Since his own administration is responsible for administering the law, that sounds a lot like a promise to sabotage Americans’ health care and blame other people for the disaster.

The point, however, is that building on Obamacare wouldn’t be hard, and wouldn’t even be all that complicated.