In this case:
"the faster it will commit demographic suicide as America becomes ever younger and more diverse"
The US is getting younger? The more diverse I won't argue with. But younger? What planet is Frank Rich on?
ETA: I think I know what he meant. I _meant_ that the membership of the GOP ends with a cohort -- the GOP is aging, and right now that aging looks irreversible. It is not the US that is getting younger. It is the GOP that is getting older. But that doesn't work with his argument because it is tautological.