“I share the opinion of you and many of your colleagues that these sanctions and the carefully constructed global consensus behind them are responsible for driving Tehran to the negotiating table. It was because sactions worked that we are starting implementation of the Joint Plan of Action, an important step – though still only a first step – toward a comprehensive solution,” Clinton wrote in the letter.

“Now that serious negotiations are finally under way, we should do everything we can to test whether they can advance a permanent solution. As President Obama said, we must give diplomacy a chance to succeed, while keeping all options on the table,” she wrote. “The U.S. intelligence community has assessed that imposing new unilateral sanctions now ‘would undermine the prospects for a successful comprehensive nuclear agreement with Iran.’ I share that view. It could rob us of the diplomatic high ground we worked so hard to reach, break the united international front we constructed, and in the long run, weaken pressure on Iran by opening the door for other countries to chart a different course.”

Clinton continued, “If the world judges – rightly or wrongly – that negotiations have collapsed because of actions in the United States Congress, even some of our closest partners abroad – to say nothing of countries like Russia and China – may well falter in their commitment.