What do young Americans want? Something different from what they've been getting from the president they voted for by such large margins. Evidence comes in from various polls. Voters under 30, the millennial generation, produced numbers for Barack Obama 13 percentage points above the national average in 2008 and 9 points above in 2012. But in recent polls, Obama approval among those under 30 has been higher than the national average by only 1 percentage point (Quinnipiac), 2 points (ABC/Washington Post) and 3 points (YouGov/Economist). Those differences are statistically significant. And that's politically significant, since a higher percentage of millennials...