Leaving aside, for a moment, their morality and policy merits, there are essentially three intellectually coherent ways to approach Syria today:
- Assad is the only hope of peace and stability in the country, given his military and political strength and the support of Iran, Hezbollah, and Russia. Defeating IS is the paramount objective. We should, therefore, ditch our previous allies and work with the Syrian government and the Russians to bring peace. This was Trump’s position during the campaign.
- Syria is hopeless. We can provide diplomatic support for peace wherever possible, but otherwise, we wash our hands of the place, because all of the other alternatives are even worse. This is Obama in 2016.
- We can bring about a solution to the Syrian problem without selling out our allies by intensifying our military involvement and thereby creating diplomatic leverage. This could include creating no-fly zones or even by sending in American troops. This is the Clinton/McCain/Graham approach.
As far as I can tell, the evolving Trump position is #2 plus taking just enough action against the government to piss off the Russians without creating any leverage for a favorable political settlement. That makes no sense whatsoever unless you assume that being incoherent and unpredictable is an end in and of itself.