We (US CIA) has provided military assistance to terrorist rebels for many years, the only reason for the CIA facility in Benghazi was to support the backchannel supply of arms to the Syrian opposition. So much for that theory.
It matters little whether it was the Syrian government (Assad) or the rebels that did the gas attack. The perception is that it was Assad, and that presented Trump with a low-risk opportunity.
I’m with you there. Power does what it wants. Nothing we can do about it, but at least we can watch it on TV.