Put it another way: When Democratic base voters flock to Sanders, they are expressing dissatisfaction what current Democratic policies. When Republican base voters flock to Trump, they are expressing dissatisfaction with Republican rhetoric.

But I said I was going to talk about what they had in common, and that’s easy enough here: whether its rhetorically or policy-wise, Trump and Sanders supporters are asking their parties to move away from the center—or, perhaps more clearly stated, away from each other.

Indeed, there are those on both sides who long for a Trump-Sanders match-up. It would, on some level, be a battle of caricatures—as defined by the opposing side. And what about the Democrats who would love to see Trump get the nomination? And Republicans who’d like to see Sanders? They envision that contest as referendum more than an election, a chance to finally and fatally eject the other side from the political spectrum. As Glenn Beck put it recently: “I think we need to just cut to the chase and have a real libertarian/conservative go up against Elizabeth Warren or avowed socialist Bernie Sanders. This country could finally make up its mind based on two honest and completely different visions of the future of this country.”