Turkey is on their own here. NATO will not stand up where the U.S. stands down. Russia can now support Assad without worrying about the U.S. getting in the way. The Kurds are already cutting deals with Assad and the Russians.
This is a terrible political position for Turkey to even think about going into Syria on their own.
>>The Kurds are already cutting deals with Assad and the Russians<<
Trump’s best option might be to tell Assad and the Russians that they may respond as they please to the Turks, and the US won’t care.
And then tell the Turks what we did.
Long term, Assad may decide that ethnic cleansing of the Sunni Arabs may make Syria more stable.