In 2007, at the Damascus Gate restaurant on the outskirts of the Syrian capital, two men met regularly with a senior Yemeni official. The restaurant was one of many places in Damascus where Yemeni business leaders, intermediaries and political figures passed through with relative ease. Syria’s visa regime made the city both accessible and discreet. What was discussed there, however, was not routine. One of the men, known as Abu Hadi, an Iranian …