Millennials, of course, are not the only supporters of these changes; nor are they especially prominent in the groups that have pushed them. But they are functioning as a tipping point in the debates nonetheless.

Polling last year by the Pew Research Center found that nearly two-thirds of Millennials support legalizing marijuana and slightly more back same-sex marriages; in each case, that was more than any older generation. The clear shift in attitudes has seeded a belief among political leaders that change on these issues is inevitable because public opinion, over time, will only tilt further as more Millennials (and their younger siblings) enter the electorate. "There is a sense that where Millennials are on a lot of these cultural issues is where things will go for years," says Kristen Soltis Anderson, a Republican pollster who studies young voters.

But if the sun is shining for Millennials on the cultural front, their economic forecast remains wintry. On Tuesday, Young Invincibles, a group that advocates for young adults, issued a bracing report that noted the unemployment rate for Millennials (which it defined as workers 18 to 34) has remained stuck in double-digits for 70 consecutive months. Georgetown University's Center on Education and the Workforce has likewise found young workers today losing ground compared with previous generations in wages, workforce participation, and net worth, with the losses deepest for younger men. Add in mounting student debt, as well as delays in family formation and homeownership, and phrases like "lost generation" don't seem excessive.

In important ways, President Obama has aimed his agenda toward this generation. Culturally, he's almost invariably aligned with them (even on marijuana legalization, the Justice Department has essentially thrown up its hands). He has promoted policies to reduce student debt, increase pressure on colleges to improve graduation rates, and expand national service—an attractive option for a civic-minded generation that has produced roughly six applications for every spot available in AmeriCorps. Obama's healthcare bill involves more complex generational accounting: It does require some healthy young people to buy more comprehensive (and expensive) insurance than they might prefer, but it also significantly shifts resources down the generational ladder by restraining Medicare spending to help fund subsidies for the working-age uninsured. The mandate that insurers allow children to stay on their parents' policies until age 26 has already covered 3.1 million Millennials.

Obama's problem is scale. Nothing on that list sufficiently confronts the magnitude of the employment crisis facing younger workers. Nor has he sufficiently challenged the federal budget's tilt from young to old, as retiring baby boomers swell spending on seniors and squeeze discretionary programs (like education and research) that benefit future generations. Congressional Republicans have shown somewhat more willingness to confront those entitlement costs, but they would direct the savings toward tax cuts that mostly benefit older workers—and that failed to produce consistent job growth under George W. Bush.