For the first time in 35 years, the United States and Iran are close to resolving key diplomatic differences.
A temporary, six-month nuclear accord between Iran and several world powers, signed in Geneva in November, begins this week and could serve as a steppingstone to a permanent resolution of the Iranian nuclear issue.
In exchange for dismantling Iran's nuclear arms program, world powers agree to provide billions of dollars in badly needed sanctions relief to the country whose economy is in crisis.
It might work — unless Congress kills it before it even has a chance to work.
The Nuclear Weapon Free Iran Act of 2013, before the Senate right now, would do just that. Impelled largely by election-year fears and powerful lobbying groups, the bill calls for reinstated sanctions if it does not dismantle its "illicit nuclear infrastructure."
But the Geneva accord allows Iran to enrich low-level uranium at levels used in nuclear power and medicine, implicitly contravening this demand of the Senate.
The bill, supported by many Democratic senators in opposition to their own president and Majority Leader Harry Reid, also demands that Iran cease most ballistic missiles test.
However, that was not a condition of the Geneva accord, making it seem that the United States — without support from its allies — is moving the goalposts in the negotiations.
If Iran does not negotiate in good faith, which is possible, the United States and its allies could, and should, impose tougher sanctions. And the fact that Congress is eager to do so might provide extra incentive for the negotiation.
But passing the bill now — right after Iran has done what was required to get to this point — would make it harder to achieve a resolution.
It would damage the ability of President Hassan Rouhani and Foreign Minister Mohamad Zarif to continue the peace process in defiance of powerful opposition in the Iranian government.
The bill ties President Barack Obama's hands at one of the most sensitive diplomatic moments for world security.
Lawmakers who were quick to censure opposition to the Iraq war as undermining the commander-in-chief seem to have no qualms about doing just that now.
The chance to negotiate an agreement with the Iranians does not come often. The pressure built from a decade of sanctions has ushered in a more moderate government that seems to have the backing of the Ayatollah.
Despite the Senate's best effort to sabotage the deal, it's a chance that we should seize.