Syrian forces already attacked by U.S. before Trump took office. The Syrian quagmire was not started by Trump. It was in full battle array before Trump took office. The Syrian mess is not Trump's doing. It is utter nonsense and foolishness to suppose Obama wanted Assad gone but was not engaging militarily against Assad.
Point being, If Congressional approval is needed now why was it not obtained under Obama? Since it was not obtained then, and we have troops already there, because Obama sent them there, then Trump has the authority to do whatever is needed to keep them as safe as possible. That includes the hindering of WMD delivery.