It often flies under the radar – until it flies into the Russian GRU’s face – but the U.S. military presence in Syria is a constant aggravation for Russian President Vladimir Putin’s government.

Russia’s particular gripe is the ongoing presence of U.S. forces in north and eastern Syria. While those forces are primarily deployed to fight the Islamic State, they also help deter Turkish attacks on Kurdish settlements, and Syrian-Russian-Iranian attacks on Sunni fighters/residents east of the Euphrates river valley. Vladimir Putin knows that until the U.S. removes its forces from Syria, he’ll be unable to ensure that Bashar Assad’s government dominates all other Syrian actors. In addition, Putin won’t be able to use his leverage over Iran in order to win concessions from the Saudis and Israel.