Much has been made of the way Bernie Sanders has galvanized young voters. Exit polls at recent Democratic Primaries suggest that he's an overwhelming favorite of Millennials (and Gen Zers, the oldest of whom will vote for the first time in 2016.)
That's great, for what it's worth. Sanders' challenge is that, even in 2008 when Barack Obama was swept into power with unprecedented youth participation, Americans under 35 were far less likely to vote than Americans over 65.
According to the latest U.S. Census estimates, there are currently about 75 million Americans 18-35 compared to 'only' 46.2 million senior citizens. IE, Americans in the age group presumed to favor Sanders handily outnumber the 65+ cohort who seem to favor Hillary Clinton.
The thing is people over 65 are about 1/3 more likely to vote than people under 35.
It seems likely that if Hillary Clinton is the eventual Democratic nominee, a lot of young voters will stay home; after all, from a purely statistical point of view, they're not committed participants in the democratic process.
That's bad news for the Democratic Party for two reasons: The party fares better in elections with higher rates of participation generally, and Democratic-leaning voters skew younger. You'd think the Democratic Party would, as a result, favor the candidate most popular with young voters.