My theory on this.Trump really wants to end this mess,why now? I have 2 ideas:

1.He has confirmation that the Clinton investigation is over,and a lot if people will be charged and therefore nobody will stop him doing so.

1. This is more likely,nobody from the power establishment counted with Turkye.Erdogan looks very determined to destroy the Kurdish militias,which will leave the US with no proxies on the ground and that means the US has to sacrifice its on soldiers,even worse,risk a direct confrontation with the Turks and losing Centcom.