David Auerbach wrote for Slate about Bernie Sanders' campaign:
Bernie Sanders is running an anti-establishment campaign, and anti-establishment candidates are not supposed to win. And yet the Vermont senator, who represents a more progressive and economically redistributionist alternative to the Democratic Party’s mainstream, is within 14 points of Hillary Clinton’s lead in national polls, narrowly lost the Iowa caucuses, and won the New Hampshire primary by a more than 20-point margin. In part because of his robust support among younger voters, in recent weeks pundits have started declaring Sanders “the future of the Democratic Party,” in spirit if not immediate electoral chances. There are a lot of plausible diagnoses for how a candidate who wasn’t even a member of the Democratic Party a year ago could now be its presidential nominee. Slate’s Jamelle Bouie pointed to the toll of the Great Recession on younger people. The Black Lives Matter movement has brought long-ignored civil rights issues to the foreground. And going forward, the death of conservative Supreme Court Justice Antonin Scalia will surely add an extra dash of chaos to both major primaries. But there is also a structural social issue that has enabled Sanders’ rise: the ability of the Internet in general, and social networks in particular, to cloister off and amplify political ideologies on the left and right alike.
Just as Fox News and talk radio carved off a group on the right that brooked our current era of no compromise, the architecture of how we consume and share information online has begun to do the same to a very different class of left-wing voters. (As we’ve all witnessed, that effect applies to mass enthusiasm outside of politics, too, building large new niches from the bottom up.) This generation has partially replaced traditional mainstream establishment narratives with localized media bubbles. And so far, the Democratic primary voters among them are rejecting Hillary Clinton in surprisingly large numbers.