Michael Hayden led the Central Intelligence Agency from 2006 to 2009 and the National Security Agency from 1999 to 2005. Olli Heinonen is a senior fellow at Harvard’s Belfer Center for Science and International Affairs and a former deputy director general of the International Atomic Energy Agency. Ray Takeyh is a senior fellow at the Council on Foreign Relations.

As negotiations between Iran and the great powers press forward, Secretary of State John F. Kerry seems to have settled on this defense of any agreement: The terms will leave Iran at least a year away from obtaining a nuclear bomb, thus giving the world plenty of time to react to infractions. The argument is meant to reassure, particularly when a sizable enrichment capacity and a sunset clause appear to have already been conceded. A careful assessment, however, reveals that a one-year breakout time may not be sufficient to detect and reverse Iranian violations.

Once the United States had an indication that Iran was violating an agreement, a bureaucratic process would be necessary to validate the information. It could be months before the director of national intelligence would be confident enough to present a case for action to the president. Several U.S. intelligence agencies, the Energy Department and national nuclear laboratories would need a chance to sniff the data to be convinced that a technical breach had occurred. Only after this methodical review was finished could the director go to the White House with conclusions and recommendations.

Given that the International Atomic Energy Agency (IAEA) would be the on-site inspection organization responsible for the verification of an agreement, the United States’ scoop would have to be forwarded to that body. Of course, both the speed and the extent of U.S. sharing would be affected by the need to protect sensitive human or technical sources of information. Only then would IAEA representatives begin talking with their Iranian counterparts about gaining access to disputed sites or activities. History suggests the Iranians would engage in protracted negotiations and much arcane questioning of the evidence. Iran could eventually offer some access while holding back key data and personnel. It would be only after tortured discussions that the IAEA could proclaim itself dissatisfied with Iran’s reaction. This process also could take months.

Should the indication of infractions originate with the IAEA, the United States would likewise want to validate the findings itself, which would also be time-consuming.

Secretary of State John Kerry said nuclear talks with Iran have made "genuine progress." (Reuters)

Once the IAEA arrived at a verdict of noncompliance, it would forward its grievances to the U.N. Security Council for adjudication. The United States would have to convince the other member states invested in the agreement — including veto-wielding Russia and China — that the accord was being violated and that forceful action was needed. Time would be spent quarrelling over divergent views, with several outcomes possible, including a Security Council presidential statement or a resolution whose content would need to be agreed upon. And only then could new economic sanctions be imposed on Iran. So, add at least a few more months.

Could sanctions really make a meaningful impact on Iran in whatever time, if any, remained in a one-year scenario? Any sanctions would take time to stress Iran’s economy, particularly in the aftermath of an agreement that paved the way for the return of trade and investment. Of course, the United States would not have to wait for the economic pressure to work and could use force against Iran without U.N. endorsement. However, since the advent of nuclear weapons, the United States has negotiated arms-control agreements with an entire spectrum of adversaries and has never used force in response to violations.

And the reality is that any cheating by Iran would always be incremental and never egregious. Throughout the duration of an agreement, there would be occasional reports of Iran enriching to unacceptably high levels and revelations of unreported nuclear installations and experimentation in weapon designs. Iran’s habit of lulling the world with a cascade of small infractions is an ingenious way to advance its program without provoking a crisis. In the end, a year simply may not be enough time to build an international consensus on measures to redress Iranian violations.

In the midst of all the typical Washington political cacophony about the progress of the negotiations, what is lost is that an accord between the United States and Iran would be the most consequential arms-control agreement of the post-Cold War period. It would determine the level of stability in the Middle East and impact global nuclear nonproliferation norms. With stakes so high, we need a national debate about the nature and parameters of any agreement. The right venue for that debate is the halls of Congress. No agreement can be considered viable or enduring without such legislative approbation.