As U.S. and Israeli officials talk publicly about the prospect of a military strike against Iran's nuclear program, one fact is often overlooked: U.S. intelligence agencies don't believe Iran is actively trying to build an atomic bomb. A highly classified U.S. intelligence assessment circulated to policymakers early last year largely affirms that view, originally made in 2007. Both reports, known as national intelligence estimates, conclude that Tehran halted efforts to develop and build a nuclear warhead in 2003. The most recent report, which represents the consensus of 16 U.S. intelligence agencies, indicates that Iran is pursuing research that could put...