Iranian Supreme Leader Ayatollah Ali Khamenei, seen here in a photo released by his official website Thursday, stopped short of giving his endorsement to the framework nuclear deal struck last week. AP hide caption

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Iran's President Hassan Rouhani, speaking in Tehran in February, has spoken out in favor of nuclear negotiations and opening Iran to the world. But he has faced criticism from hard-liners at home. Ahmad Halabisaz/Xinhua/Landov hide caption

itoggle caption Ahmad Halabisaz/Xinhua/Landov

Secretary of State John Kerry (left), and Russian Foreign Minister Sergey Lavrov (right) wait for the start of a meeting at the Beau Rivage Palace Hotelin Lausanne, Switzerland, on Sunday to discuss a nuclear deal on Iran. Brendan Smialowski/AP hide caption

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Secretary of State John Kerry delivers a statement about the recently concluded round of negotiations with Iran over their nuclear program at the International Olympic Museum in Lausanne, Switzerland, on Saturday. Brian Snyder/Reuters/Landov hide caption

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Tom Cotton, R-Ark., the freshman senator and Harvard graduate senator with a record of tough talk on foreign policy. Carolyn Kaster/AP hide caption

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A letter from U.S. senators suggests the lawmakers "not only do not understand international law, but are not fully cognizant of the nuances of their own Constitution," says Iranian Foreign Minister Mohammad Javad Zarif. Kyodo /Landov hide caption

itoggle caption Kyodo /Landov

Israeli Prime Minister Benjamin Netanyahu speaks before a joint meeting of Congress on Capitol Hill in Washington on Tuesday. Netanyahu said the world must unite to "stop Iran's march of conquest, subjugation and terror." House Speaker John Boehner of Ohio (left) and Sen. Orrin Hatch, R-Utah, listen. Andrew Harnik/AP hide caption

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U.S. Secretary of State John Kerry (right) and Iran's Foreign Minister Javad Zarif (left) shake hands as Oman's Minister for Foreign Affairs Yussef bin Alawi (second from right) and the former EU top diplomat Catherine Ashton watch in Muscat, Oman on Nov. 9. Iran is holding talks with six world powers in Vienna this weekend in advance Monday's deadline for a deal on Iran's nuclear program. Nicholas Kamm/AFP/Getty Images hide caption

itoggle caption Nicholas Kamm/AFP/Getty Images

Secretary of State John Kerry (right) and Iranian Foreign Minister Javad Zarif shake hands as Omani Minister Responsible for Foreign Affairs Yussef bin Alawi and former EU top diplomat Catherine Ashton watch Nov. 9 in Muscat, Oman. Nicholas Kamm /AFP/Getty Images hide caption

itoggle caption Nicholas Kamm /AFP/Getty Images