It was designed to send a message without pissing off the Russians.
it their attention i guarantee you it did.trump wants out of syria
This was my thinking. Trump had to do something to prove he means what he says, but it didn't have to be effective. It had to look like he took the problem seriously, and it had to serve as a warning, but it absolutely needed to be measured so as to not provoke the Russians into doing something stupid.
It's political drama, and that was what it was intended to be.