Chris Hayes makes in his excellent book, Twilight of the Elites, between “institutionalists,” who want to make existing institutions function better and “insurrectionists,” who want to tear them down and start again.
Sanders is an insurrectionist. That’s why, asked about following the most transformational liberal president in a half-century, he didn’t say that America is moving in the right direction but has further to go. He said America needs a “political revolution.” He also said that, “America’s campaign finance system is corrupt.”
Hillary never talks that way. She acknowledges problems but she rarely indicts America’s core economic and political institutions. Consider the two candidates’ answers on financial regulation. Sanders said that, “Wall Street, where fraud is a business model, helped to destroy this economy and the lives of millions of people.” Thus, “we have got to break up” the banks. Hillary, by contrast, said that “Dodd-Frank was a good start, and I think that we have to implement it … We have to save the Consumer Financial Protection board.” Sanders, in other words, attacked the system; Hillary explained how it could be improved.
.. Progressives don’t just love him because his policy proposals are more left wing than Hillary’s. They love the fact that he calls America’s political and economic system corrupt, and that he refuses to play by that corrupt system’s rules: for instance, by raising money via a super PAC. That’s why being a “socialist” doesn’t hurt Sanders among many liberals. For many, “socialism” is just another way of saying you want to tear down the existing order and build something better in its place.