Preventing a nuclear weapons-capable Iran has always been a bipartisan priority. And it can only be achieved through bipartisanship. We worry, therefore, that this cooperative spirit has been severely, but not irreparably, eroded in recent days. It is crucially important that it be revived.

Past Congresses have played an important role in ratcheting up pressure on Iran’s leadership by increasing economic sanctions. These measures have passed with overwhelming bipartisan majorities in both chambers due to laudable partnerships. The ongoing P5+1 negotiations, which we believe represent the best opportunity to reach a solution to Iran’s drive for nuclear weapons capability, were made possible by these Congressional actions.

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That is why we also strongly believe that a good deal can only be achieved if both the executive and legislative branches are involved in crafting and approving it. Tehran wants sanctions relief in return for nuclear concessions. The president can eliminate sanctions created by executive orders, but he can only waive congressional sanctions, for 120 days at a time, which comprise 13 out of 20 total sanctions against Iran. Only Congress can fully repeal the significant number of sanctions it put in place; therefore, Congress must play a critical role in achieving a lasting deal.

Indeed, Iran is unlikely to make meaningful reductions for the sake of temporary relief that requires repeated presidential waivers, especially with a new administration only two years away. We believe eschewing the legislative branch only weakens U.S. negotiators’ hand.

While lawmakers are right to insist that any deal receive Congressional consideration, that is a message best delivered to the White House by a bipartisan coalition, and not to Iran’s Supreme Leader by 47 Republicans. Lawmakers are working on legislation that would give Congress a say, but to pass, and withstand a veto, it will have to be bipartisan.

Bipartisanship is critical for another reason too: preserving credibility in the coming public debate about the deal. It has become a mantra, repeated by the administration and Congress alike, that “no deal is better than a bad deal.” Working with the Bipartisan Policy Center, we have previously laid out the principles we believe should guide negotiators, as have other experts. But no serious public debate has taken place about what constitutes a good deal, what concessions are worth making and which are just too dangerous.

With no established standard by which to judge a deal, the public will either have to examine the merits of a deal themselves or turn to trusted experts. Any deal will be enormously complicated, both technically and procedurally. It will involve arcane conditions on centrifuge numbers, connections and type as well as enrichment levels, stockpiles and fuel conversions. It will detail processes for conducting inspections, shipping enriched uranium out of Iran and nuclear fuel to it, and for the phased lifting of sanctions and implementation of nuclear reductions. Anybody who has not immersed themselves in the details of nuclear engineering and arms control will be hard-pressed to arrive at an informed judgment about whether the deal meets the specific goal laid out by the president—pushing Iran’s timeframe for producing a bomb’s worth of weapons grade uranium out to at least a year—or even the more general goal of putting in place verifiable reductions that will prevent Iran from sprinting to a bomb.

Who, then, will be able to credibly assess and discuss a deal? The bipartisan coalition of congressional skeptics could have, but we fear that recent partisanship might have frayed it too much. And Republicans, standing on their own, have unfortunately now ensured that they can too easily be cast by the deal’s supporters as political grandstanders rather than principled and informed opponents.

One lesson we should have learned from the invasion of Iraq is that momentous national security decisions should not be made without critical examination and debate—both in Congress and in public—of the underlying facts and assumptions. Our political system was created with power divided between the branches because the process of deliberation and discussion is the best guarantee of sound decision-making. That process should be respected.

For the sake of ensuring that any deal the United States agrees to strengthens its national security, it is critical that we recover the spirit of cooperation—between both parties and branches—that has been missing of late. One option would be for congressional leaders and the president to create an independent review panel, similar to the 9/11 Commission or National Defense Panel, to assess how any deal would impact Iran’s nuclear capabilities. This would signal a renewal of collaboration and ensure that the American public is provided with objective information needed to judge the deal’s merits.

Both Capitol Hill and the White House should realize that good Iran policy can only come from good process. And getting the process right will require bipartisanship and cooperation.

Robb was governor of Virginia from 1982 to 1986 and served in the U.S. Senate from 1989 to 2001. Wald  was deputy commander of the U.S. European Command from 2002 to 2006. They are the co-chairs of the Bipartisan Policy Center’s National Security Project.