Turkey’s decision to invade northern Syria earlier this week has put the US in a tricky position. On the one hand, the Turkish forces were attacking an ISIS city, which they like, but then they attacked Kurdish forces in Manbij, who just captured the city recently after a 2+ month US-backed offensive.
The US was already struggling to handle several “pro-US” factions in Syria fighting one another, and Turkey just adds to that. Vice President Joe Biden was in Turkey this week, however, pledging unconditional US support, both for their post-coup purge and for the Syria offensive.
Keeping Turkey placated is now job one for the US in Syria, which is a big shift because until recently they just had to keep them satisfied enough to not risk losing access to the Incirlik Air Base, from which they’d been launching strikes in support of the same Kurds turkey is now there to fight.
Though the US appears to hope that keeping Turkey happy will mean their operation inside Syria will mean they will join the fight against ISIS in earnest, all comments out of Turkey indicate that ISIS is a very secondary objective, and that fighting the Kurds to chase them out of former ISIS territory is job one.
How the US manages that remains to be seen, but it’s hard to see how they’ll be able to keep the Kurdish YPG on board with their coalition even as it becomes increasingly clear that Turkey comes first.