Abstract: The American airstrike against Iranian-backed fighters near Al Tanaf base last month represent a major change in the nature of the United States’ use of force in Syria. Despite the aggressive stance adopted by the White House, the rest of the administration oppose opening a broader front against Iran in Syria before the end of the Mosul and Raqqa battles. Meanwhile, Iran is advancing and challenging the established “frontlines” with Russian support. The Syrian conflict is at a critical juncture that will determine whether Iran or the United States enjoys influence over Iraq and Syria. Without an effective anti-Iran strategy in Syria, Tehran will come to dominate the land corridor through Iraq, Syria, and Lebanon.