What happens in the next five years may be just as important to Kathleen Sebelius’ legacy as what she did in the last five. That’s because the law she helped shepherd into existence as secretary of health and human services, the Affordable Care Act, remains very much a work in progress.

By one crucial and fundamental measure, the law is living up to its name: More Americans now have access to affordable health care. Enrollment in the Obamacare exchanges started slowly but has hit 7.5 million, with at least 3 million people newly covered by Medicaid and another 3 million young adults on their parents’ plans. The latest estimates predict that by 2016, 25 million Americans will have health insurance who otherwise wouldn’t.

This is no small achievement, and to reach it Sebelius had to overcome the law’s unwieldy structure. Its combination of subsidies, penalties and inducement was the result of political bargaining with an array of powerful and stubborn constituencies. Making it all work would have been an ambitious undertaking in any environment. But Sebelius wasn’t working in just any environment: The Affordable Care Act was hounded from the outset by a Republican Party that defined itself largely by its relentless opposition to the law — in Congress, the courts and the states.

As more Americans get insurance because of the law, this kind of knee-jerk opposition to it will inevitably decline. That’s not to say, however, that the law can’t be improved upon; its long-term success remains an open question. One of its main goals, for example, was to reduce costs, and it’s simply too soon to tell whether the recent slowdown is the result of the law — or, if it is, whether that slowdown will last.

Even if the law succeeds on all counts, Sebelius’ legacy will inevitably have to contend with the disastrous launch of HealthCare.gov, a mostly self-inflicted failure at the worst possible moment. The website, which was visited by 4.7 million people on its first day but allowed only six to sign up, was eventually fixed. But it did lasting damage to not only the administration’s reputation but also the idea of governmental competence.

Now the task of repair and improvement will fall to Sylvia Burwell, the well-regarded director of the Office of Management and Budget who President Barack Obama has nominated as Sebelius’s replacement. Burwell will have responsibility for the success of the Affordable Care Act — and in many ways she’ll be the keeper of Sebelius’ legacy.

Editorial by Bloomberg View