The Sunni-Shiite civil wars in Iraq and Syria are both nearing their end, and in both cases the Shiites have won — thanks largely to American military help in Iraq's case, and to a Russian military intervention in Syria. Yet Russia and the United States are not allies in the Middle East. At least not yet.
U.S. President Donald Trump may get in bed with the Russians and the Shiites eventually, but he doesn't seem to have given the matter much thought yet. So for the moment U.S. policy follows the line laid down by Barack Obama.
U.S. President Barack Obama was determined not to send American troops into another Middle Eastern war. Even as the Sunni extremists of Islamic State and the Nusra Front (al-Qaida under another name) expanded their control in Syria and then seized much of Iraq, Obama restricted the U.S. intervention to training local troops and deploying American air power.