Nationally, the conflict between the brown and gray arises partly over immigration policy but primarily over government spending. Aging whites now provide huge electoral margins for a Republican Party committed to retrenching government, while minorities preponderantly back a Democratic Party defending public investment. It’s telling that even the budget cuts the two parties have agreed on so far largely protected entitlements (which mostly benefit seniors) and squeezed discretionary programs (which offer more for young people).

Demography offers no break from these pressures. Minorities, for the first time, will likely make up a majority of newborns this year. Frey calculates that the number of people in their childbearing years is falling for whites and rising for minorities. That means the browning of the youth population will accelerate, even as the white share of seniors declines only slowly.

The irony is that security for the gray requires opportunity for the brown: Unless America can equip its young people to obtain good-paying jobs, Social Security and Medicare will face increasing financial strain. As usual, Americans will rise or fall together, even if no one acknowledged that inescapable interdependence from the tea party stage last weekend.