The main supplier of arms to the Syrian regime is the state-owned Russian weapons manufacturer Rostec. Rostec also sells weapons to the United States.
If the US had the slightest interest in degrading the military capabilities of Assad, they could easily begin by punishing the company that is arming him, cancelling all contracts, and making it illegal to do business with them.
Assad censors, monitors, and controls internet access in Syria by means of technology supplied by a US company, Blue Coat, which provides the same technology to the Gulf states, Egypt, and elsewhere.
There is simply no legitimate question about the US wanting to overthrow Bashar; he is covertly supported, and the US has openly stated that they intend to keep him in power, if perhaps, restricting his territorial control to lay the groundwork for the partitioning of the country into a handful of mini-states, as per the plan recommended by the Israelis in the 1980s