Preventing Iran from achieving nuclear weapons capability is the most urgent national security challenge facing the United States. In a February 2012 report, Meeting the Challenge: Stopping the Clock, a Bipartisan Policy Center Task Force called for a robust and comprehensive triple-track strategy: the simultaneous pursuit of diplomacy, sanctions, and visible, credible preparations for a military option. The report cautioned that while tough sanctions are important, time is of the essence and could run out before sanctions take full effect. Their goal is not to damage the Iranian economy but to force the Tehran regime to cease its nuclear program. We urge Congress to assess and report at regular intervals the progress of Iran’s nuclear program to determine the degree to which sanctions are forcing Iran to slow down or cease nuclear development.