LONDON — AS bad as things in Washington are — the federal government shutdown since Tuesday, the slim but real potential for a debt default, a political system that seems increasingly ungovernable — they are going to get much worse, for the United States and other advanced economies, in the years ahead.

From the end of World War II to the brief interlude of prosperity after the cold war, politicians could console themselves with the thought that rapid economic growth would eventually rescue them from short-term fiscal transgressions. The miracle of rising living standards encouraged rich countries increasingly to live beyond their means, happy in the belief that healthy returns on their real estate and investment portfolios would let them pay off debts, educate their children and pay for their medical care and retirement. This was, it seemed, the postwar generations’ collective destiny.

But the numbers no longer add up. Even before the Great Recession, rich countries were seeing their tax revenues weaken, social expenditures rise, government debts accumulate and creditors fret thanks to lower economic growth rates....