I understand that the cool kids are not supposed to talk about electability right now, since everyone understands that this is just code for “I hate Bernie.” So far I’ve been a good boy and stayed away from this, but I’ve long had one very specific problem with Bernie Sanders’ electability. It has nothing to do with his socialist views, though. It has to do with his supporters.

As we all know, support for Sanders is highest among the young, and Sanders has explicitly said that his election strategy depends on generating high turnout among the young. But here’s the thing: every four years, for as long as I can remember, I’ve heard promises that this is the year we’ll finally get young people to turn out for us. But they never do. Overall turnout goes up and down depending on the election, but 18-29 year olds always make up 17-19 percent of the voting population. Always.

In a new paper, David Broockman and Joshua Kalla use the detailed results of a huge new survey and conclude that Sanders can indeed do as well against Trump as more moderate candidates, but only if he makes up for lost votes among older voters by motivating young voters to turn out in unprecedented numbers:

If this is true, it’s a real problem. Sanders hasn’t increased turnout in the primaries and caucuses so far, and to have a chance in the general election he’d need youth turnout to be well over 50 percent. That’s never happened in recent history. Even Barack Obama in 2008 couldn’t quite manage it.

I’ve never been a big fan of Sanders, but I try to remain fairminded about measurable quantities. Youth turnout is just such a thing, and it’s one that I’m sensitive to since I long ago became cynical about promises of getting young people to vote in larger numbers than usual. Maybe Bernie can finally do it. But I wouldn’t bet the ranch on it.