Unable to reach a deal by the self-imposed June 30 deadline, negotiations over Iran’s potential nuclear weapons program were wisely extended to July 7. While the date has changed, the parameters of an effective, albeit imperfect, deal should not.

As a guidepost, U.S. envoys should give strong consideration to an influential open letter from a bipartisan cohort of national security experts that was released by the Washington Institute for Near East Policy. The group, which includes five former members of President Obama’s administration, does not reject negotiations, but rather expresses concern over inking an ineffective deal. And while the letter may put the administration even further on the defensive, it should not be read as an affront. In fact, it can be an asset in negotiations with Iran, as well as in convincing Congress that an eventual deal deserves approval.

“Most of us would have preferred a stronger agreement,” the experts state. Among the limitations noted is that the interim agreement, if adopted, would not prevent Tehran from having nuclear weapons capability, nor would it force the theocracy to dismantle its nuclear enrichment infrastructure. But the experts do acknowledge that the framework would “reduce that infrastructure for the next 10 to 15 years. And it will impose a transparency, inspection and consequences regime with the goal of deterring and dissuading Iran from actually building a nuclear weapon.”

Despite the limitations, a deal is better than the alternatives, which include military options. The talks should continue despite the recent recklessness from Ayatollah Ali Khamenei, Iran’s supreme leader, who pronounced new Iranian red lines that would likely be unacceptable to the U.S. and possibly England, France, Germany, Russia and China (the “P5+1” group negotiating with Iran).

Other key issues the group identified include strong provisions on monitoring and verification by the International Atomic Energy Agency, possibly including military facilities. The writers also called for “strict limits” on advanced centrifuge research and development, testing, and deployment over the first 10 years that the agreement is in place. And sanctions relief should reflect verifiable steps, with snapback sanctions as a backup for noncompliance, too, they wrote.

Other aspects of the letter are important, including a U.S. affirmation of its policy to prevent Iran from developing or acquiring a nuclear weapon, as well as advice on taking regional foreign and defense policy initiatives “to check Iran and support our traditional friends and allies.”

On Tuesday, Obama encouragingly reaffirmed that Iran must live up to the tentative agreement in order to finalize a deal. “I will walk away from the negotiations if in fact it’s a bad deal,” he said.

For now, final judgment should be reserved until a final deal. And critics should acknowledge that rejection could isolate America from the P5+1, which could mean that Iran gets some sanctions relief while still maintaining its nuclear capacity. For now, the hope is that the extra time talking — and listening — will produce an acceptable, if not ideal, accord.