I think Gerdler is approaching the point but primarily the issue is our standing with our allies in the region and not much else imo. It's a big win for Russia that stems from the syrian civil war.

While iraq feels that america has tampered with their sovereignty and they wish to expel us, the turks have said politically motivated assassinations are a war crime.

When we established the syrian safe zone, and pulled our troops out, we established a front against isis where traditional enemies (turkey and iran) held the front together with russian support. Meanwhile iran was making several regional allies and fighting for courtship of Iraq's new government.

A move like this, as indicated by a rare meeting between assad and putin, is a bad move for our foothold in the region. It sets the stage for iraq and turkey to turn their backs on us, while traditional allies such as Britain complain about not being informed.

Turning our backs on kurdish fighters in syria also set the stage for a saudi operation there. We've basically lost every ally in the region beginning with the destruction of the iran nuclear deal and finishing here. Without the feeling of the us protecting their sovereignty, it seems highly likely that everyone will turn to russia to restore confidence against threats like isis.