First- The exceptionally long-lived baby boomer generation, which will live well into their late 80's.
Second - The Childlessness epidemic amongst millennials guaranteeing the population will dramatically shrink. And the gendered political polarization between sexes will persist well into their extremely old age as well, thus locking in the already bifurcated pattern of politics.
And both of these social forces are hitting at the same time. People ask why I have inherently gloomy prospects for Westen society, it's because despite the economic affluence the sociology is catastrophic.