As far back as 2012, John McCain was advocating the arming of Syrian rebels. And he continued that call through 2013 and beyond. For some reason, folks in Washington paid attention to that. Here, John McCain was advocating arming the same folks who killed American troops.
He even went to Syria and took a picture with them.
And so, we sent small arms over to Syria. And what happened?
A particular segment of the rebels -- ISIS -- consolidated a bunch of the territory in Syria, including oil wells, using some of those arms. This allowed them funding, and an extended campaign across Syria and into Iraq, raiding the Iraqi Army of its American-made vehicles and weapons - military equipment that was only there because of Senator McCain's support for an invasion of Iraq in the first place.
In many ways, all the moves that Senator McCain supported allowed ISIS to form and grow. There is no organized insurgency in Syria. Rebels fight with rebels who fight with rebels. There was no possible course of action that would have allowed moderate rebels to fight ISIS. That is simply the words of something afraid to admit their opinions on Syria have let to chaos in Iraq.