$British Foreign Secretary Philip Hammond, 2nd right, U.S. Secretary of State John Kerry, right, and European Union High Representative for Foreign Affairs and Security Policy Federica Mogherini, left, talk to Iranian Foreign Minister Mohammad Javad Zarif as the wait for Russian Foreign Minister Sergey Lavrov, not pictured, for a group picture at the Vienna International Center in Vienna, Austria, Tuesday, July 14, 2015. After 18 days of intense and often fractious negotiation, world powers and I$

British Foreign Secretary Philip Hammond, second from right, U.S. Secretary of State John Kerry, right, and European Union High Representative for Foreign Affairs and Security Policy Federica Mogherini, left, talking with Iranian Foreign Minister Mohammad Javad Zarif, second from right, were posing for a group picture at the Vienna International Center on Tuesday after a landmark deal was reached to curb Iran’s nuclear program. (The Minnesota Star Tribune)

Opinions will vary on the deal announced Tuesday between Iran and the "P5+1" (the United States, the United Kingdom, France, Russia and China — the five permanent members of the U.N. Security Council — plus Germany). But all should acknowledge that the beleaguered international system worked as designed in producing an agreement on Iran's potential nuclear weapons program. Global leaders recognized the threat that a weaponized Iran posed, and through strict sanctions the P5+1 brought Iran into a multilateral negotiating process that resulted in an accord. So a major global challenge was addressed, however imperfectly, without war. Diplomacy produced results.

As Congress considers its response over the next 60 days, it should keep in mind that this isn't just about Iran, but also about maintaining the capacity of the international system to coalesce on critical matters, despite tensions and disagreements on so many other geopolitical issues. Rejecting this kind of engagement will make it much more difficult for subsequent presidents to achieve similar results.

Lawmakers should also consider what may follow if diplomacy fails. If Congress should reject the deal, the U.S. might be blamed for allowing Iran to escape from sanctions without having to complete its end of the bargain.

And all should consider what successful implementation might mean: An Iran with a reduced capacity to dash for deployment; a Mideast not further destabilized by a nuclear arms race that Iranian deployment would surely spur, and, just maybe, at least a chance of improving relations with a nation that has been an adversary for over three decades.

Skepticism toward the deal, and certainly toward Iran, is understandable. Iran has been designated a state sponsor of terror, and has destabilized Iraq, Syria, Yemen and Lebanon. America's strongest regional ally, Israel, rightly considers Iran an existential threat. So do many of America's Gulf allies.

Indeed, it is precisely the nature of the regime that makes this accord so important. President Obama, who in his statement said the deal was "not built on trust, it is built on verification," offered "extensive briefings" to members of Congress. They should take him up on that.

Obama should also continue to reach out to the American people to explain why the agreement is in the national security interest.

And he should reassure Mideast allies that the deal, and any subsequent rapprochement with Tehran, will not come at their expense.

It's disappointing to have so many lawmakers and presidential prospects — mostly along sharply partisan lines — rejecting the deal even before they had a chance to digest it. Based on the broad outline, it appears close to the initial framework agreed upon last spring. Close questions are needed on several issues, especially on the exact nature of the inspection regime, and how to counter any Iranian backsliding.

But now is the time for cautious and sober consideration, not reflexive politics. The threat is too significant, and the promise of revived diplomacy too great, for anything less.