From Informed Comment
Trump is slapping sanctions on Turkey for invading northern Syria after Trump told Turkish president Tayyip Erdogan that it would be all right for him to invade northern Syria.
It is really difficult to be an analyst of foreign affairs in the age of Trump, because we try to understand policy moves with regard to their logic. Much of what Trump does seems illogical.
Trump's loud clown circus has so dazzled and confused cable news that few are even reporting this about-face as a puzzle in need of explanation.
How to explain his sanctions on Erdogan for doing what Trump told him it would be OK to do? Offhand, I can think of three possible explanations:
1. Trump may just be mentally unbalanced and so does contradictory things because of his condition.
2. In this case, the sanctions may be a political cover. Trump is being pilloried by Republican stalwarts (though not mostly those still actually in office) for his abrupt retreat from Syria. What he did makes him look weak and threatens to damage his blustery brand.
Announcing sanctions on Turkey at least creates an image of strength and push-back. It also puts him on the same page with Sen. Lindsay Graham and other GOP Syria war hawks who have called for sanctions on Turkey.
Remember, Trump's "sanctions" may also be just tough talk. Trump on many occasions has slow-rolled sanctions legislated by Congress, as on Putin's Russia, or simply declined practically to implement them. As of now, aside from some tweets, there is no early prospect of Turkey being sanctioned in practical terms.
3. It could be a shadow-play orchestrated behind the scenes by Russian President Vladimir Putin. We suspect that Putin has some sort of hold over Trump. It so happens that Trump's green light to Turkey's Erdogan to invade has caused the Democratic Union Party in Kurdish Syria to fold and beseech the Russians and the Syrian government to come up to the northeast and take control of the border with Turkey.
Putin would see this development as a windfall, but the problem is that he would not want to deploy his air force against Turkish forces. Russia and Turkey in Syria are rivals and foes, but have attempted to work out the conflict via their proxies. Nor should I think the Syrian Arab Army of Bashar al-Assad wants to try to go toe to toe against the much bigger and massively better armed and trained Turkish army.
So the best way for Assad and Putin to assert themselves would be to promise to patrol the Syrian-Turkish border themselves so as to allay Turkish concerns about terrorists coming across from Syria into the Kurdish areas of southeast Turkey. I don't think such an offer will dissuade Erdogan from his social engineering project of ethnically cleansing Kurdish villages down to about 20 miles from his border and then planting fundamentalist Sunni Arab Syrians there, giving them the Kurdish homes and land so that they can spy on the Kurds and keep them from infiltrating over to Turkey.
I should underline that in the above paragraph I am explaining Turkey's point of view; I don't personally believe there is any evidence that the Democratic Union Party or its paramilitary, the People's Protection Units (YPG) have engaged in terrorism against Turkey. Whether they have given safe haven to persons from the Kurdistan Workers Party of Turkey, (the PKK), whom both Turkey and the US view as terrorists, I cannot say. But I do believe that Turkey's equation of the Democratic Union Party with the PKK is wrong-headed and unjustified.
So it is now useful to Putin to have the US put pressure on Turkey to get back out of Syria, and you could imagine him getting word to Trump to strong-arm Erdogan.
This last scenario would explain why Trump pulled this about face in sanctioning Turkey. He seems eager not to tangle with Erdogan, but has throughout his presidency been far more eager to do Putin's bidding.