President Barack Obama may be on the verge of striking a historic deal to limit Iran's nuclear program - that is unless Democrats scuttle it.

Yes, you read that right.

Some Democrats, determined to repeat the deadly errors of the Bush years, are considering siding with right-wing Republicans to undermine Obama's diplomacy that could potentially lead our nation into another war in the Middle East.

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Case in point: There are currently two pieces of legislation in the Senate - one backed by Sens. Mark S. Kirk, R-Ill., and Robert Menendez, D-N.J.; the other pushed by Sens. Bob Corker, R-Tenn., and Lindsey Graham, R-S.C. Both are poison pills that could very well kill any chance for diplomacy.

Progressives are watching carefully for any Democrat who signs on to these measures, mindful that a diplomatic resolution with Iran would allow our nation to begin climbing out of the still-smoldering wreckage of President George W. Bush's failed foreign policy in the Middle East.

Let's look at the origins of this current impasse. Last November, soon after six world powers and Iran announced an extension of negotiations aimed at limiting Tehran's nuclear program, Senate Republicans and a solitary Democrat boasted about their plans for a new diplomacy-killing Iran sanctions bill.

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At the time, we urged Democrats to stay far away from this legislation, co-sponsored by Kirk and Menendez, arguing that passing new sanctions at any point during the negotiations would almost certainly lead to a collapse of the talks and the likelihood of another war in the Middle East. We said clearly that blame would lie squarely with any Democrat who supported this new sanctions bill, because without Democrats, Republicans wouldn't have enough votes to override the president's veto.

The White House and progressive activists denounced the bill and Menendez and a handful of Democrats wisely backed off - temporarily. But Menendez and company haven't backed down entirely, and continue to threaten to bring the legislation back as early as late March.

While Menendez and his Democratic accomplices in the Senate claim they are trying to help the president by threatening to pass new sanctions, Republicans continue to reveal their true intentions. One GOP senator said recently the "intended consequence" of any new Iran bill is to "end the negotiations." And now, with Speaker John A. Boehner's, R-Ohio, outrageous invitation to Israeli Prime Minister Benjamin Netanyahu to speak before a joint session of Congress shortly before Israeli elections, Republicans are turning the U.S. Congress into a prop for another country's election and doubling down on their attempt to undermine diplomacy with Iran.

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Additionally, the bill championed by Corker and Graham would throw impossible-to-meet procedural hurdles in the way of successfully cementing an agreement. Unfortunately, five Democrats - including Menendez and Sen. Tim Kaine, D-Va., are original co-sponsors of the legislation, which was introduced last wee.

The danger remains acute and bears repeating: Both the Menendez/Kirk and the Corker/Graham legislation could well kill diplomacy. If a sanctions bill passes while talks are ongoing or Congress makes it impossible to guarantee implementation of a final deal reached by the president, the negotiations will be dead and the United States will be seen as the spoiler.

In either scenario, the international coalition pressuring Iran would fracture, and we could be on the path to war.

If these talks fail because of unwarranted congressional meddling, Democrats who side with Republicans will be at fault. And progressive activists will hold them accountable for the rest of their careers in politics.

The United States is facing a historic opportunity to make the region and the world more secure without resorting to war. We agree with our allies, negotiating partners and scores of national security experts: Congress should hold its fire and let diplomacy work.

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Anna Galland is the executive director of MoveOn.org Civic Action. Becky Bond is the Political Director of CREDO Action. They wrote this for CQ-Roll Call.