A proposal by Connecticut Sen. Chris Murphy and his Democratic colleague, Sen. Dianne Feinstein of California, backed by a cadre of other like-minded senators, presents the best legislative option to promote a successful outcome in the nuclear negotiations with Iran.

Murphy's resolution reaffirms that the United States will not accept a nuclear-armed Iran and pledges that harsh sanctions will be imposed immediately if Iran violates the terms of the current negotiations, cheats on a final agreement, or fails to acquiesce to a nuclear deal by the stated deadline.

What the resolution does not do - and rightly so - is impose, trigger, or schedule new sanctions on Iran. That ill-conceived alternative is the preferred tactic of a group of impatient ideologues whose simplistic worldview led to a decade of war in Iraq.

The outcome of the debate between these two sides in the weeks ahead will determine whether there is a dangerous confrontation or a chance for peace in the Persian Gulf.

Imposing new sanctions, or even threatening to do so, poses an unnecessary risk to the fragile ongoing talks between Iran and the world powers currently working with the United States. Iranian negotiators may well walk away from this historic opportunity under the threat of needless saber-rattling by our legislators. Iranian President Hassan Rouhani is under immense pressure from hardliners back home to blow up the talks and return to a path toward conflict.

The danger goes beyond an Iranian tantrum - legitimate or not. If Congress indicates that it does not take the nuclear negotiations seriously, it risks undermining our credibility with our NATO allies who are our essential negotiating partners. The global sanctions regime that brought Iran to its knees did so precisely because it was a global effort; American leadership produced this effective alliance, but American ambivalence could cripple it.

Congressional posturing must not give fair weather partners like Russia and China the chance to walk away from the coalition and resume profitable trade with Iran. Preserving a united global community that takes the threat of nuclear proliferation seriously is essential for maintaining pressure on the Iranians during the conversation and reactivating the full sanctions regime if necessary.

For Congress to jeopardize the talks with new sanctions is to turn back the clock on a year's worth of progress.

In the words of Israeli Brigadier General Uzi Eilam, "This is the time for diplomacy."

Murphy and his colleagues have epitomized the best of American engagement with the world, standing for smart diplomacy backed, as always, by the credible threat of forceful action.

If the day comes when talks with Iran fail, Congress stands ready to punish Iran accordingly. Until then, however, we must take advantage of a historic opportunity to win the day at the negotiating table.