To put it another way: Can you think of one way that Bernie Sanders is signaling respect to voters outside of his base?

He has taken a nearly maximalist liberal position on every major issue. It’s especially striking from him, because he has shown over his career that he grasps the importance of building a coalition…

Now, though, Sanders has evidently decided that progressives will no longer accept impurities — or even much tactical vagueness. He, along with Elizabeth Warren, has embraced policies that are popular on the left and nowhere else: a ban on fracking; the decriminalization of border crossings; the provision of federal health benefits to undocumented immigrants; the elimination of private health insurance.

For many progressives, each of these issues has become a moral litmus test.