Excerpts of an op-ed published in The New York Times

Iran’s leaders are acting as if they have not received that message. In recent weeks, the president of Iran, Hassan Rouhani, has declared that his government will not dismantle a single centrifuge. Tehran also went beyond words by testing long-range ballistic missiles that could reach American military bases in the Middle East, as well as our ally Israel. It has even dispatched warships to sail close to the maritime borders of the United States in the Atlantic Ocean.
We also know the Iranians have worked to deceive us in previous rounds of negotiations.
In 2003, when Mr. Rouhani was Iran’s chief nuclear negotiator, Tehran issued a declaration that it was suspending uranium enrichment and other nuclear activities. Last year, as he ran for president, Mr. Rouhani even boasted that Iran had flouted the agreement.
Offering inducements is not enough. Diplomacy must be backed by a clear choice for the Iranian government: Either it dismantles its nuclear program so that it lacks a pathway to weapons capability or it faces greater economic sanctions and international isolation. Without this clarity, no one can be surprised if Iran rejects diplomatic overtures.
We strongly believe that the assertion by Congress of its historic role in foreign policy can, in fact, complement and enhance the administration’s efforts by forcing Iran to recognize the stark implications of intransigence. The president should welcome such congressional initiatives, which would actually strengthen, not weaken, the hand of his administration in forthcoming negotiations.