A merican President George W. Bush has signed legislation that lets his country and India cooperate on civilian nuclear-energy programs. The move is likely to be one of the legacies of Mr. Bush's presidency: It is the cornerstone of his attempt to forge a new relationship between the two countries.

Unfortunately, the agreement also represents a sharp reversal of nonproliferation policy when the United States has put the fight to stop the spread of weapons of mass destruction at the heart of its foreign policy. U.S. policymakers have backed Mr. Bush, but Indian Prime Minister Manmohan Singh may find the domestic political battles sharper, even though the deal will likely be approved in Delhi, too.

India's determination to maintain its nuclear options has meant that the country remains outside the Nuclear Nonproliferation Treaty. That decision allowed India to develop a thriving domestic nuclear industry and its own nuclear weapons, but it foreclosed cooperation with other countries such as the U.S. and Japan on nuclear issues and limited India's foreign-policy options more generally.