Critics of the interim agreement suggest that we wait for sanctions to have more bite. But while we wait, Iran’s stockpile of fissile materials will grow, and the Arak reactor moves closer to completion. Another alternative would be to bomb the Arak reactor and Iran’s enrichment facilities. This option will remain available, but why choose it – and the negative consequences that might follow – if diplomacy can limit Iran’s stocks of fissile material and keep the Arak reactor off-line? The interim agreement curtails Iranian nuclear-related activities in ways that sanctions have been unable to accomplish, without having to resort to military action, and all of the unintended consequences that might follow.

A great deal is being made about extending the timeline in which Tehran could break out from the interim agreement’s constraints. Extending the breakout timeline has clear value, less for military action than for helping intelligence analysts to piece together systematic evidence of noncompliance. The interim agreement’s monitoring provisions could help greatly in this regard. Absent this accord, detecting breakout would be a far more serious problem.

In the coming months, we can expect differing interpretations over some aspects of the interim agreement, including the modalities of inspections. There will be a constant drumbeat of criticism over what hasn’t been accomplished. There will be unconfirmed reports that Iran is covertly cheating. Skeptics on Capitol Hill will seek steps that could have the practical effect of derailing the negotiations.

Interim deals are necessary when the whole enchilada is just too big to swallow. But interim deals can raise the stakes for a final deal, and the longer the wait, the harder it becomes. Take, for example, the 1972 Interim Agreement between the United States and the Soviet Union, which couldn’t get a handle on MIRVs. It took seven years for the second Strategic Arms Limitation Treaty to be negotiated, during which there were ceaseless charges of Soviet cheating on US interpretations of the Interim Agreement’s provisions, as well as worrisome Soviet behavior unrelated to the terms of the agreement. SALT II’s slim chances in the Senate disappeared when a small group of decision makers in the Kremlin decided to invade Afghanistan. The moral of this story: Negotiate the follow-on accord as quickly as possible, especially since (1) critics will argue that the interim agreement doesn’t accomplish enough, and (2) the agreement won’t curtail bad behavior unrelated to the agreement. A negotiating process with Iran that seeks further piecemeal deals will only whip up predictable opposition at each step and is unlikely to withstand these pressures.

All of which makes the pursuit and particulars of a final deal brutally difficult. The interim deal hints at no dismantling of existing nuclear infrastructure, curtailment of existing uranium enrichment capacity and the freezing of a parallel plutonium track to nuclear weapons. The Obama administration will have to do better than this.