i don't often go into this deeper level of analysis, and don't be surprised if i don't pull it out again until close to the election, but you can broadly split american politics (and most politics in the satellite states, including canada) down this dividing line, between the rhodes clique (the aristocracy, who remain powerful at the un) and the birchers (the bourgeoisie, most importantly the koch brothers). the parties are both messy big tents, and don't really mean much. but, you see sides develop more readily when you look at the candidates' backgrounds, and it's easy to predict how they're going to legislate, regardless of what they actually say.
that's why this mayor pete is probably going to be in the same governing philosophy as clinton - an internationalist that wants to outsource foreign policy to the united nations (which i would support), is in favour of "free trade" (which i would not support), is in support of bringing in low wage workers from other countries (which i would not support) and says nice things about black people while legislating against them (which i would not support). if you're a black or latino democrat, you should rightfully be wary about a guy that was educated by a group designed to maintain the priority of the british aristocracy in the commonwealth, however bizarre those words might look to you on paper. you went through this with clinton. maybe you didn't really understand it then, but you have the opportunity to, now.
so, if you can split the spectrum this way, what about sanders?
as with everything else, he doesn't align; i see no evidence that either side has ever co-ordinated with him at all. if somebody shows me some, i'll change my mind. but, as it is, it's a part of the reason he's still exciting.