In December of 2015, Congress did something rare: It passed a law, with bipartisan support, that President Obama signed and conservatives are championing. The Every Students Succeeds Act, known as ESSA, rolls back federal authority in local schools and limits the reach of the secretary of education. Yet the bill received unanimous support of Democrats in both houses of Congress, as well as support from most Republicans. The law aims to replace the widely loathed, crippling “cookie-cutter” testing regulations imposed by No Child Left Behind, and it’s being implemented for the first time this school year—the first test for ESSA’s efficacy. But some of its conservative supporters say they’re worried the reforms could be hampered if Republicans lose control of Congress.

Indeed, the law’s future may be uncertain given the interpretative license available to whichever party wins the White House and Senate. “The next administration has the constitutional responsibility for ensuring that the law is enforced,” Education Secretary John King told reporters Wednesday in response to concerns about shifting interpretation of the law. Not yet fully field tested, ESSA is still basically a bipartisan victory—because Democrats and Republicans remain free to interpret it differently.