Following the invasion of Iraq by the U.S and the overthrow of Saddam Al-Qaeda was easily able to establish a foothold in Iraq. They formed Al-Qaeda in Iraq (AQI). Al-Qaeda also formed Al-Nusra (Or Qaeda in Syria) after the Syrian Civil war started. AQI split to form ISIS in 2013/14.

Al-Nusra was able to secure weapons from other rebel groups (as well as clandestine support through the Gulf States which are U.S allies and as such supplied U.S made weapons to them). While ISIS was able to route the Iraq army capture stockpiles of American weapons.

This wonderfully intertwined several narratives. One: Prevailing conspiracies from the predominately Shia groups in Iraq and Iran. This goes that the U.S created ISIS to destabilize the middle east to weaken Iranian and Iraqi power.

Surface level knowledge of those who are aware of U.S foreign policy through out history: The supporting of the Mujaheddin against the Soviets, the support of the Muslim Brotherhood against Baathist governments etc...

Finally the idea that strong dictators are needed to keep these countries in order.

Right so now you have a Baathist (Arab Nationalist) regime supported by Iran and Iraq literally fighting Al-Qaeda and ISIS which if you've watched Fox News for at least 5 seconds you'd think are the biggest threat to the American way of life since WW2. And they're fighting with U.S manufactured weapons. This is why the Alt-Right loves Assad and Russia.

That's why there's large alt right support for Assad.