All the projections that suggest Sanders can't win the nomination and the election suppose that a large slice of his supporters (or people who would support him if they could be reached) just won't bother to vote — and that's a pretty save bet.
The scholarly and experimental work on registering non-voters and getting them to the polls shows that this is an incredibly hard problem that no one has any great solutions for. And yet, with so many non-voters in every Congressional district and every electoral race, every race is a toss-up if you include them in. Bringing out non-voters was behind some of the great political surprises of the past decade: Dean, Obama, Trump, Corbyn, etc.
The fact that we don't know how to get nonvoters to the polls doesn't mean Bernie can't win: it means we know what Bernie has to do to win. Knowing is half the battle.
The key for Sanders's political revolution to succeed, then, is to find some way to mobilize the 23 percent of voters who are mislisted or unlisted. But though Jackman and Spahn's research confirms that this group exists, and is more liberal than America as a whole, it's unclear if campaigns could cost-effectively reach them and persuade them to vote.
A recent study by Notre Dame's David Nickerson makes this point well. Between 2004 and 2007, he conducted field experiments in six cities (Detroit, Tampa, Kalamazoo, Denver, Memphis, and Louisville) meant to reach previously unregistered voters and sign them up.
In each case, a local nonpartisan group hired canvassers to walk down certain streets and knock on every door. If every resident in the house was registered, the canvasser moved along. If someone was unregistered, the canvasser would help them register. If no one answered, the canvasser would do another sweep or two to try to reach them. Nickerson assigned "treatment" streets to be canvassed and compared them with nearby "control" streets that didn't get canvassed. In three of the experiments, he also made sure that wealthy, middle-class, and low-income streets were all canvassed, so he could compare effectiveness among them.
The canvasses did increase the number of registered voters — but not by a lot. On average, each treated street led to 10 newly registered people, a 4.4 percent increase. But only two of those people would go on to vote. The increase in registration was greater on poor streets, and the increase in turnout was greater on rich streets.
(via Naked Capitalism)