The initial nuclear agreement with Iran represents a historic break in the cycle of escalation between our two countries. If it leads to a comprehensive deal, we could permanently take war and an Iranian nuclear weapon off the table. There’s only one catch: the agreement requires that we abstain from imposing new sanctions on Iran, and many in Congress are still working to pass new sanctions.

However, there is a way for Congress to enhance our diplomatic leverage and flexibility—without blowing up the talks. The authority to trade in existing sanctions for Iranian nuclear concessions has become muddled after more than three decades of legislation. To facilitate a comprehensive deal, Congress could pass a sanctions “kill switch” that syncs up waiver authorities for the president, providing clear-cut assurances that we can deliver on our end of the bargain.

The danger that Congress refuses to take “yes” for an answer from Iran and ends up sabotaging the deal is still very high. Senators Robert Menendez (D-NJ) and Mark Kirk (R-IL) were reportedly working to force a vote on a new sanctions bill with waivers that could delay implementation for six months, though that plan is apparently on ice until at least next year. According to Sen. Menendez, “sanctions that are invoked six months from the date of enactment…create the flexibility for diplomacy.”

This stance puts Menendez and others in open opposition to the president and our nation’s negotiators. As the White House has made clear, if Congress passes new sanctions—even if they include waivers to delay implementation—both Iran and the international community would see the United States as violating the terms and faith of the agreement. After the deal collapses, Iran would once again have an unconstrained nuclear program, we would lose our unprecedented inspections regime, and the U.S. and Iran would be back on a pathway to war.

The chief leverage that the U.S. and other members of the P5+1 have in negotiations is not unending sanctions, but sanctions relief. Since 1979, the United States, European Union and UN Security Council, for a variety of purposes, have levied more than thirty separate sanctions on Iran. However, the United States has led the charge. Most of America’s unilateral sanctions on Iran are codified via both Executive Order and Congressional legislation. That includes nine separate Congressional sanctions, including measures targeting Iran’s oil and financial sectors that are the most valuable relief we can offer. As a result, it is extraordinarily difficult to unwind the sanctions on a permanent basis because the president cannot do so unilaterally—he would need Congressional support.

Right now, the president only has the authority to offer significant temporary sanctions relief, and has exercised that authority to obtain the first phase agreement. But temporary and reversible relief will not be enough to strike the final agreement. Iran is unlikely to agree to part with its key nuclear leverage unless we are willing—and able—to part with our sanctions leverage. And with Congress stuck on autopilot pushing new sanctions, the president’s diplomatic flexibility is in serious doubt.

That’s exactly why a sanctions kill switch could be such a valuable diplomatic tool. Congress would pass a legislative vehicle that enables the president to not just waive sanctions for a few months, as virtually all Congressional sanctions permit, but to repeal them on a permanent basis at a time of his choosing. Such a mechanism would require the president to certify to Congress that Iran has reached a final agreement that will satisfy international concerns regarding its nuclear program. Then, the president would be able to exercise sunset clauses within the kill switch for each of the separate Congressional sanctions. That way, the administration can sequence relief to correspond with Iran’s implementation of nuclear concessions like the adoption of the IAEA’s Additional Protocol and additional measures to tie Iran’s nuclear program to its peaceful nuclear needs.

This would provide the administration maximum flexibility and leverage to obtain Iranian concessions because Iran would have faith that the president can deliver. With a clear path to sanctions relief, any attempt by Iran to reject a viable final agreement that doesn’t demand total Iranian capitulation would be a clear indication that it is Iran, not the United States, that is blocking progress toward a deal.

Congressional skeptics should imagine the alternative scenario: what if Congressional refusal to lift sanctions scuttles a deal that would permanently prevent proliferation to Iran, ultimately leading to an Iranian nuclear weapon, war, or both? That would be the ultimate tragedy—an entirely preventable one.

Ryan Costello is a Policy Fellow with the National Iranian American Council.