Hillary Clinton's Arab Spring policy was to give support to any group trying to take out a Muslim dictator, no matter who they were. This took out Libya's dictator, Egypt's and several others. Yemen's President had to flee his nation, and it is in civil war.
Al Assad had Russian backing because of Russia's large naval base there. Anyone aware of the geo-politics knew Russia would defend the leader letting it have its only major naval base on the Mediterranean. Clinton either didn't care to know or didn't care after knowing.
She armed Islamic fundamentalists who drew support from ousted Saddam military leaders, and they became ISIS. As they started to carve an Islamic theocratic state out of Iraq and Syria, she still armed them because she considered Assad worse. Obama continued these policies after she was no longer Secretary of State.
The biggest mistakes the Democrats made were:
* assuming that all dictators are bad and that democracy will bloom if you just remove them
* that anyone fighting a dictator is good
* not bothering to follow up on who you arm is using the weapons
* that Russia wouldn't protect its investments or not caring to think about the implications