In practice, the administration’s willingness to envision a new role for Hezbollah in the Middle East, combined with its desire for a negotiated settlement to Iran’s nuclear program, translated into a reluctance to move aggressively against the top Hezbollah operatives, according to Project Cassandra members and others.

Lebanese arms dealer Ali Fayad, a suspected top Hezbollah operative whom agents believed reported to Russian President Vladimir Putin as a key supplier of weapons to Syria and Iraq, was arrested in Prague in the spring of 2014. But for the nearly two years Fayad was in custody, top Obama administration officials declined to apply serious pressure on the Czech government to extradite him to the United States, even as Putin was lobbying aggressively against it.

Fayad, who had been indicted in U.S. courts on charges of planning the murders of U.S. government employees, attempting to provide material support to a terrorist organization and attempting to acquire, transfer and use anti-aircraft missiles, was ultimately sent to Beirut. He is now believed by U.S. officials to be back in business, and helping to arm militants in Syria and elsewhere with Russian heavy weapons.