Obama has an ambitious second-term agenda, which, at least in broad ways, his campaign is beginning to highlight. The President has said that the most important policy he could address in his second term is climate change, one of the few issues that he thinks could fundamentally improve the world decades from now. He also is concerned with containing nuclear proliferation. In April, 2009, in one of the most notable speeches of his Presidency, he said, in Prague, “I state clearly and with conviction America’s commitment to seek the peace and security of a world without nuclear weapons.” He conceded that the goal might not be achieved in his lifetime but promised to take “concrete steps,” including a new treaty with Russia to reduce nuclear weapons and ratification of the 1996 Comprehensive Nuclear Test-Ban Treaty.

In 2010, Obama negotiated a new Strategic Arms Reduction Treaty with the Russians and won its passage in the Senate. But, despite his promise to “immediately and aggressively” ratify the C.N.T.B.T., he never submitted it for ratification. As James Mann writes in “The Obamians,” his forthcoming book on Obama’s foreign policy, “The Obama administration crouched, unwilling to risk controversy and a Senate fight for a cause that the President, in his Prague speech, had endorsed and had promised to push quickly and vigorously.” As with climate change, Obama’s early rhetoric and idealism met the reality of Washington politics and his reluctance to confront Congress.