America�s top negotiator in the Iran nuclear talks offered a surprisingly detailed assessment of Tehran�s existing nuclear capabilities on Monday as she warned that failing to secure a final deal with the longtime adversary would seriously threaten American national security.

The remarks by Wendy Sherman, the undersecretary for political affairs at the State Department, come at a pivotal juncture in U.S. politics as Democrats and Republicans on Capitol Hill wrangle over provisions in a new bill allowing Congress to review a final agreement.

Sherman, speaking at the Religious Action Center of Reform Judaism in Washington, said that failing to reach an agreement would leave Tehran closer than ever to acquiring a bomb.

Without a deal, Sherman said, Iran would expand its nuclear enrichment program to 100,000 centrifuges in the next few years instead of shrinking that figure to 5,000 as agreed in the framework agreement brokered in Lausanne, Switzerland on April 2.

She also said Iran could produce enough weapons grade plutonium to produce two bombs each year. And in terms of uranium enrichment, the country could expand its already significant stockpile of 10 tons of enriched uranium.

In dealing with both of the emerging pathways to a bomb, she said an agreement would result in Iran having �zero weapons grade plutonium� and a stockpile of enriched uranium that is reduced by 98 percent. She added that if the U.S. backs out of a deal widely viewed as fair, international support for sanctions will whither away.

�So when you look at the comparison to the agreement we are negotiating and the chance that we wouldn�t succeed � the better course of action is abundantly clear,� she said.

Many lawmakers on Capitol Hill, to put it mildly, disagree. Critics note that President Barack Obama and Iranian President Hassan Rouhani have portrayed the framework deal in markedly different ways to their domestic constituencies, with Rouhani saying any final deal will include immediate sanctions relief instead of the gradual lifting of sanctions.

At the moment, Democratic and Republican leaders are haggling over the best way to insert themselves in the international negotiations.

On April 14, the Senate Foreign Relations Committee voted unanimously in support of legislation that would halt the president�s ability to implement a deal with Iran for 30 days while Congress reviews the deal. Committee chairman Bob Corker (R-Tenn.) was able to win over Democratic support by watering down his original proposal, a compromise that forced the White House to back off its veto threat on the bill.

However, a number of pro-Israel hawks in Congress want to reinsert those original provisions � and add other ones � when the bill reaches the Senate floor. Sen. Marco Rubio (R-Fla.), for instance, filed an amendment last week that would require Iran to publicly recognize Israel�s right to exist as a part of any deal � something the Islamic Republic is virtually certain to reject.

Democrats, such as Sens. Chris Coons of Delaware and Barbara Boxer of California, have threatened to reverse their support for the Corker bill if Republicans attach new amendments that tilt the legislation to the right.

Debate on the amendments is scheduled to begin on Tuesday.

During Sherman�s Monday speech to the Union for Reform Judaism, which represents more than 900 congregations across North America, the senior diplomat also reiterated the Obama administration�s concerns about statements made by Israeli Prime Minister Benjamin Netanyahu ahead of the Israeli elections in March.

�If the new Israeli government is seen as stepping back from its commitment to a two-state solution � that makes our job in the international arena a lot tougher,� Sherman said, referring to Netanyahu�s pre-election promise to never allow for the creation of a Palestinian state, which he later reversed.

She noted that Washington�s previous ability to push back against European efforts to internationalize the conflict at the United Nations �depended on our insistence that the best course in achieving a two-state solution is through direct negotiation between the parties.�

 

This article was written by John Hudson for Foreign Policy on April. 27, 2015. John Hudson is a senior reporter at Foreign Policy and co-author of the magazine's �The Cable� blog where he reports on diplomacy and U.S. national security issues. Prior to joining FP, John covered politics and global affairs for The Atlantic magazine's news blog, The Atlantic Wire. In 2008, he covered the August War between Russia and Georgia from Tbilisi and the breakaway region of Abkhazia.