The Supreme Court’s dramatic decision to uphold the Affordable Care Act gives President Barack Obama a major political victory. But the controversial measure now becomes a major election issue and its future will remain in doubt at least until voters render their verdict this November.

That’s because presumptive Republican nominee Mitt Romney has pledged to scrap the plan Obama hopes will become his lasting political legacy, something he would be in position to do if he unseats the incumbent and fellow Republicans keep the House and win the Senate.

“If we want to get rid of Obamacare, we’re going to have to replace President Obama,” Romney declared after the decision, denouncing the plan as “a job killer” that would raise taxes and increase the deficit and vowing he would do on the first day of his presidency “what the court did not do.”

On the other hand, Thursday’s 5-4 decision means that an Obama re-election victory would probably ensure that the plan enacted after a bitter 15-month battle remains on the books, despite continuing resistance by congressional Republicans and many GOP governors.

Similarly, a split electoral verdict in which Democrats at least retain the Senate will make it harder for a Republican president to scrap the plan, though he might be in position to change and possibly cripple it.

Obama called the decision “a victory for people all over the country whose lives will be more secure because of this law,” citing specific benefits like those protecting people with pre-existing conditions and warning critics against refighting the political battles of two years ago.

He acknowledged that, even if he wins, the plan likely will face changes over time. In fact, no one really knows how its complex details will work, and it also remains unclear whether it will succeed in slowing the soaring costs of health care as the goal of universal coverage is pursued.

Beyond its impact on America’s health programs, Thursday’s decision will have a major impact in defining the Supreme Court tenure of Chief Justice John Roberts. By joining the court’s four liberal members to uphold the Obama law, Roberts underscored his promise during confirmation hearings to approach cases with “no agenda,” rather than from an ideological viewpoint

Conservative critics had counted on the court’s five Republican appointees to reject the measure’s key mandate requiring all Americans to purchase health insurance through private companies, regional networks or a federal alternative or be subject to a payment.

Ironically, that concept was initially a Republican idea and was part of the plan Romney enacted in Massachusetts, as Obama observed Thursday.

The mandate is crucial because it provides the funding to pay for extending health insurance to more than 30 million Americans who lack it today.

But though Roberts questioned the constitutional authority for it in last March’s oral arguments, he joined with the four Democratic appointees to uphold it, not under the constitutional authority to regulate interstate commerce but under the taxation authority.

Though the decision settled the issue of the law’s constitutionality, the reaction made clear it won’t come close to ending the bitter debate over the degree to which the federal government should regulate the nation’s health care.

If Romney wins, he has vowed that, on day one of his presidency, he would grant all 50 states waivers to opt out of the federal program and would follow that up with legislation to kill the plan through the same budget reconciliation process Obama used in 2009 to get his bill through the Senate.

That procedure bars unlimited debate and means that 51 of the 100 senators can act, instead of the 60 needed to surmount the Senate’s filibuster rules.

Ironically, the court appears to have given the GOP nominee an additional campaign weapon to use against Obama by defining the required payment for those forsaking insurance as a tax. Republicans immediately noted that Obama had promised his plan would not raise taxes on middle-class Americans.

In the end, despite feverish rhetoric by critics, any hope of getting rid of the Obama plan now rides almost totally on the election results. But the nation still faces major health care issues, and Thursday’s decision makes it more likely that Obama’s Affordable Care Act will be the vehicle to deal with them.

Carl P. Leubsdorf is the former Washington bureau chief of the Dallas Morning News.