But this fact might say it better than any: In the 2016 campaign, Sanders won more votes among those under age 30 than the two presumptive major-party presidential nominees combined. And it wasn't close.
The above chart comes from a report by the Center for Information and Research on Civic Learning and Engagement (CIRCLE) at Tufts University. It shows more than 2 million young people cast ballots for Sanders in the 21 states that voted by June 1 and where exit polls included data on the youth vote.
Clinton and Donald Trump combined? Less than 1.6 million. Sanders, in fact, won about 29 percent more votes among those under the age of 30.
And that number actually rose as the campaign went on. Back in mid-March, we looked at the same numbers and found Sanders had about 25 percent more votes than Trump and Clinton combined. And despite Clinton effectively locking up her party's nomination around that point and Trump's opponents starting to drop out, Sanders actually extended his advantage late in the campaign.
It's also worth noting in all of this that Sanders's domination among young voters has caused this surprising stat: To this point in the campaign, for the states where we have exit polls of young voters, more young people have voted for the presumptive GOP nominee for president than the Democratic one. Yes, that's right: Trump has more youth votes than Clinton.
That, of course, is not because Trump did great among young people. It's because Sanders was a phenomenon -- and perhaps also because Clinton has work to do with young people. It won't be the case in the general election, either. Even if young voters don't turn out as strongly for Clinton as they would have for Sanders, a Republican hasn't won the youth vote since 1988, and the margins have become massive.
There's no reason to expect that to change. A Washington Post-ABC News poll last week showed 75 percent of those under age 40 viewed Trump unfavorably, compared with 58 percent for Clinton. And 58 percent viewed Trump strongly unfavorably, versus 33 percent for Clinton.