Arkansas’s Obamacare Medicaid expansion has been a costly misadventure. The expansion has been so misguided in fact, that lawmakers voted earlier this year to end it, effective December 31, 2016.

That hasn’t stopped state bureaucrats from scurrying to institute a new component of expansion that makes the program even worse.

By upholding the legality of insurance subsidies on the federal exchange, the Supreme Court secured President Obama’s legacy of expanding access to health care. Now Mr. Obama must secure the other fundamental legacy of the Affordable Care Act: controlling health-care costs.

Over the holiday weekend, The New York Times published a lengthy piece confirming and adding to what has been increasingly clear for months: All over the nation, health plans being offered through Obamacare’s exchanges are requesting sizable rate hikes. In particular, popular plans that had attracted large customer bases by offering relatively low rates seem to be pushing for big increases next year, based on filings so far.

The administration’s victory in the latest Obamacare case, King v. Burwell, has relieved Congress of the need to quickly repair or replace the Affordable Care Act. But that does not mean Congress should sit back and wait for the 2016 election and a Republican president to fix the law. In fact, Republicans may have an easy way to reach their policy objectives, in a manner that might attract bipartisan support and even a signature from President Obama.