One of the best ways to track Iran's priorities in Syria and Iraq is to follow the movements of one of its highest-ranking military leaders, Maj. Gen. Qassem Soleimani. In April 2016, the commander of the Islamic Revolutionary Guard Corps' (IRGC's) elite Quds Force was spotted in the northern Syrian governorate of Hama as loyalist troops, backed by Iran, geared up for a difficult fight with rebel forces on the outskirts of the provincial capital. Five months later, he made an appearance south of Aleppo just before loyalist forces launched the final offensive that led to the critical city's capture. This month, Soleimani is on the move once again. On June 12 the elusive figure paid a visit to Iranian-led militia units on the border between Syria and Iraq, giving prayers of thanks for their recent victories in the area. His presence is telling of the newest phase unfolding in Syria's...