In a challenge to the White House, the nation’s nuclear weapons laboratories have warned Congress that federal programs to extend the life of the nation’s aging nuclear arsenal are insufficient to guarantee the viability of the weapons for decades to come. The warning, which implicitly endorsed the idea of creating an expensive new generation of more reliable nuclear warheads, has no direct bearing on the new arms control agreement reached this week by the United States and Russia. Rather, it addresses a long-simmering debate on what steps the United States should take to ensure confidence in the destructive capacity of...