“LET OBAMACARE FAIL,” President Trump tweeted Tuesday morning. Has there ever been a more cynical abdication of presidential responsibility? Mr. Trump is apparently indifferent to the pain that sabotaging the individual health insurance market would cause millions of Americans. Congress must therefore act responsibly.

Barring some totally unforeseen developments in Congress, Mr. Trump’s breezy promise to repeal and replace the Affordable Care Act has evaporated — and Senate Majority Leader Mitch McConnell (R-Ky.) previously acknowledged the GOP’s responsibility if such a circumstance came to pass: “If my side is unable to agree on an adequate replacement, then some kind of action with regard to the private health insurance market must occur,” he said earlier this month. In other words, his Republican majority finally would have to reach out to Democrats to help shape and pass a bill to repair, not replace, Obamacare.

Several moderate Democrats have recently expressed openness to reforming Obamacare in concert with Republicans, and Senate Minority Leader Charles E. Schumer (N.Y.) on Tuesday morning endorsed bipartisan cooperation to stabilize insurance markets. If Mr. Schumer is serious, he should appoint a panel of Democrats who are willing to cooperate to serve as his side’s negotiators. Those on the more reasonable end of the Senate GOP caucus have begun sounding the right notes, too. Sen. Susan Collins (Maine) called over the weekend for engaging with Democrats. From his recovery bed, Sen. John McCain (Ariz.) insisted Monday that “the Congress must now return to regular order, hold hearings, receive input from members of both parties, and heed the recommendations of our nation’s governors.” The Senate is learning, again, that it is hard to govern this country from anywhere but the center.

If enough people in each of the two parties accept that Obamacare is here to stay and that it requires fixes, the next agreements would come fairly easily. The House and Senate Republican health-care bills contained a variety of provisions that would have shored up existing individual health insurance markets. Those can be copied and pasted into a new, bipartisan bill.

Democrats and Republicans should be able to support reinsurance programs, which provide a financial backstop to insurers against customers with very high medical costs, thereby lowering premiums. They should fully fund a program that helps low-income people pay out-of-pocket health-care costs, as Trump-administration-induced uncertainty around this program has roiled insurance markets. In return, Democrats would have to give Republicans something, such as expanding state options to experiment with health-care policy and possibly some loosening of Obamacare regulations.

(Jenny Starrs/The Washington Post)

Both sides might unite around a plan that automatically enrolled everyone into at least a basic health-care policy, with a provision allowing people to opt out. The individual mandate that all Americans carry health coverage also needs to be strengthened to draw more people into the insurance system. Those concerned about the mandate’s infringement on individual liberty might be more comfortable if government tax benefits were withheld from, rather than fines applied to, people who declined to maintain coverage.

Moving beyond the partisan goal of replacing Obamacare in fact would unlock a much wider range of options, because lawmakers would no longer be bound by strict parliamentary “reconciliation” rules. Only one option should be taken off the table: the president’s irresponsible call to wreck the system.