Key moments in the unraveling of Iran's nuclear deal

FILE - In this July 14, 2015 file photo, from left to right: European Union High Representative Federica Mogherini, Iranian Foreign Minister Mohammad Javad Zarif, Head of the Iranian Atomic Energy Organization Ali Akbar Salehi, Russian Foreign Minister Sergey Lavrov, British Foreign Secretary Philip Hammond and U.S. Secretary of State John Kerry pose for a group picture after world powers and Iran struck a landmark deal to curb Iran's nuclear program, at the United Nations building in Vienna, Austria. The decision Tuesday, Jan 14, 2020, by European nations to trigger a dispute resolution mechanism in the Iran nuclear deal marks the latest step in the unraveling of the accord, which began when President Donald Trump walked away from the agreement and began restoring sanctions on Iran.