Much of the implementation of President Obama’s signature health-care law is being left up to states, according to a new report published Tuesday by the Brookings Institution’s Center for Effective Public Management. As our colleague Karen Tumulty writes in today’s paper:

State elected officials have moved in partisan directions as they have exercised their options within the law. Among those choices: whether to expand their Medicaid programs to cover the poor, whether to set up their own health insurance exchanges or rely on the federal one, and how aggressively to promote the new coverage options.
Most Democratic governors have built their own state exchanges, expanded their Medicaid programs, and are devoting intense effort toward making the Affordable Care Act work. Generally, their efforts have been proceeding relatively smoothly thus far.
GOP-led states, on the other hand, are mostly leaving it up to the federal government — whose exchange has been plagued by technical problems. And in some instances, Republican state officials have been placing obstacles in the way of the law.

About 5 million people fall into the so-called “coverage gap” — they live in states that have not expanded Medicaid coverage, they make too much money to qualify for Medicaid and they’re not old enough to qualify for Medicare. Here’s where they live: