I think he is a democratic socialist which is a slightly different thing. More like a Scandinavian socialist (note - wealthiest societies in the West so nothing to fret too much about economically).
The CO thing isn't worrying to me in a single instance, but with him it's a pattern. Sometimes a problem is something you have to respond to, regardless of the fact you have to compromise your ideals. Sometimes you get war because you are so much set on avoiding it. This is also Obama's problem. Putin pushes because he thinks Obama won't push back.
I think Sanders believes you can ignore the hard problems by shutting your eyes.
Even so, if it was a choice between Sanders and Trump, I go Sanders. But what a poor set of alternatives that would be.