Reuters reports the U.S. is concerned about air attacks on our Kurdish allies in Syria, which killed 18. It is thought the Syrian air force did the attack, although it could have been Russians.
I don't believe the U.S. has much influence with either possible perpetrator. On the other hand, it should be possible to get the Kurds some Russian-made manpad rockets - man-portable air defense systems - and the training to use them effectively. If Kurds don't get U.S. manpads, we don't get the blame.
The Kurds would be happy to have the ability to return fire when blitzed from the air. It would tend to lower the likelihood of a repeat performance.