Elizabeth Warren is, I think, a great demonstration of the kind of movement-oriented model-wielding power from within the Senate. Over and over, she's rallied tons of people to battles that they don't normally get involved in.

When [Bernie] Sanders was challenged about how he would pass his visionary ideas after he became president, he talked about if lawmakers look out the window and they see a million people marching, it changes their calculus. Well, here's an opportunity to continue working to organize these million people even if he is not the one in office.

An organization is great if you have a clear vision to be able to make it powerful. If you don't, an organization can kind of sap energy that could go elsewhere.

There is a question as to whether these rallies [2016] are going to stop in the fall. I think they should continue. They are a tremendous display of energy but also a source of energy, because people come out of them ready to fight.

What he [Bernie Sanders] does next will really determine whether he is blazing a trail that others can follow into office, or whether he is an exception to the rule.