Originally published in The Wall Street Journal, April 13, 2015

Early this summer the Supreme Court will render a decision on King v. Burwell, the case challenging the IRS workaround that allows ObamaCare subsidies to be paid through federal exchanges. Many on the right believe that if the justices rule against the administration, it would be the final stake in the heart of ObamaCare. Nothing could be further from the truth.

Millions of Americans would lose their federal subsidies and therefore be unable to pay for expensive ObamaCare coverage. In that case we can expect President Obama to declare immediately a crisis that can only be fixed by more government. As Rahm Emanuel, the president’s former chief of staff, once said, you never want a serious crisis to go to waste.

If the court rules against him, President Obama’s response will be diabolically simple and highly effective. He will ask Congress to pass a one-sentence bill allowing the subsidies to flow through federal exchanges. At the same time he will offer governors a contract to convert their federal exchanges into state exchanges with a simple stroke of a pen.

He will also mobilize his massive national political operation. It is easy to imagine the advertising campaign that will promote his simple solutions and viciously attack any opposition. Heart-wrenching examples of Americans who have benefited from ObamaCare—and there are millions who have, through taxpayer subsidies—will flood every TV channel.

The mainstream news media will ignore or contest the stories of those millions who lost their coverage because of ObamaCare and who now find health insurance very unaffordable. Without an effective response from Republicans, there is little doubt that the crisis would allow President Obama to permanently cement ObamaCare in place.

The first goal of a Republican strategic response must be to prevent President Obama’s cynical use of the coming crisis from working. If Republicans wait, we will have no chance of countering Mr. Obama’s response. We must be ready to come swiftly to the aid of those who will be victimized once again by ObamaCare if the court rules against the administration. Republicans must come together now, agree on a legislative solution, and take that solution to the American public immediately.

Second, our legislation must give America another “bite at the apple”—one last chance to repeal ObamaCare and replace it with patient-centered, market-based health-care reforms. We must set up the 2016 presidential election as a contest between health-care decisions made by Washington politicians and bureaucrats and reforms that put patients back in charge.

A number of Republicans in Congress have been diligently working together to develop a response and craft a solution, but they have not yet rallied around a single plan to offer as legislation. My own view is that the complexity of ObamaCare has done damage to America, so we should strive for simplicity. We must acknowledge the reality that subsidies cannot be ended immediately—neither practically nor politically—and a reasonable transition period is required. ObamaCare made the health-insurance market an expensive and uncertain mess. Our solution should make insurance more affordable and produce greater certainty.

Building upon these principles, and with time running out, I am introducing a simple plan that I hope can gain consensus. It combines a bill originally co-sponsored by 43 Republican senators in 2013, the “If You Like Your Health Care Plan, You Can Keep It Act,” with the elimination of some of the most harmful components of ObamaCare.

Unlike ObamaCare, it would enact a true grandfather clause. Americans could keep their current health-care plans, and the taxpayer subsidies available through ObamaCare would continue until August 2017. New enrollments in ObamaCare would be allowed, but only current enrollees would qualify for subsidies—the expansion of ObamaCare subsidies would end.

In exchange for this concession, which temporarily fixes the mess created by the sloppily written and unlawfully enforced ObamaCare, the American people should be allowed to reclaim some of the freedom ObamaCare denies them.

This bill repeals the individual mandate, ending the IRS’s enforcement of penalties—that is, taxes—imposed on law-abiding Americans who exercise their right not to purchase health insurance. It repeals the employer mandate, ending the forced shifting of millions of Americans to part-time work.

Finally, it eliminates the mandated coverages that have driven up the cost of health insurance and forced millions of Americans to lose plans that they liked and could afford.

Unlike the Patient Protection and Affordable Care Act, this legislation would live up to its name: “Preserving Freedom and Choice in Healthcare.” It would reverse many of the negative unintended consequences of ObamaCare and pave the way for its full replacement in 2017.

This is a plan Republicans should get behind now. If we wait until the ruling in King v. Burwell is handed down, it might be too late.

Mr. Johnson is a Republican senator from Wisconsin.