This generational shift draws modest public debate. But it alarms some policy advocates, who say the United States is reducing vital investments in the future.

Because Democrats and Republicans can't reach a grand bargain on deficit spending — with mutually accepted spending cuts and revenue hikes — Social Security, Medicare and Medicaid keep growing, largely untouched. Steady expansions of these nondiscretionary "entitlement" programs require no congressional action, so they flourish in times of gridlock.

Meanwhile, many discretionary programs are suffering under Washington's decision-by-indecision habits, in which lawmakers lock themselves into questionable actions because they can't agree on alternatives.