In many states, young voters gave Sanders somewhere between a quarter and a third of his votes, despite never making up more than a fifth of the electorate. This matters for future primaries because these voters aren’t going anywhere – physically or politically.
At the risk of stating the obvious, most younger voters are not going to die in the next four to eight years. That means almost all of Sanders’s voters will be around for the next contested Democratic presidential primary. Clinton’s voters, on the other hand, tend to be much older and some might be slowly replaced by younger, more liberal voters between now and the next campaign cycle.
Also, young voters might stay liberal. Political science research has shown that events in someone’s late teenage to early adult years can have a lasting impact on their long-term political preferences. It’s impossible to tell the future, but events in this primary and general election could cement these younger voters’ liberalism for years to come.
Sanders’s appeal to young voters -- an appeal a future candidate might mimic -- is partially based on policy. Many young people were rocked by the Great Recession and have no Cold War era gag reflex when it comes to terms like “socialism.” That makes voters this age warmer to very liberal economic policies. But I would bet -- and I’m stepping out of the data and into my own experience for a moment -- that Sanders’s style also plays a role. People my age have been the target of a ceaseless stream of ads (TV, Internet, etc.) since birth, and most of them (including many political ones) reek of 50-year-old advertising pros who think millennials buy anything that has a meme and some Internet slang attached to it. I would guess that Sanders’s unvarnished, on-message, issues-only style appeals to people my age by providing a break from that. Some future progressive candidate might do well by imitating that style.
A future liberal candidate would also want to win liberal voters -- some of whom are young, but some of whom are older. Not surprisingly, Sanders has done very well with this group.