But mainland residents should not look smugly at Puerto Rico. Across America, dozens of cities, counties and states may be heading down the same financial rabbit hole. Illinois, New Jersey, Philadelphia, St. Louis and Jacksonville, Fla., to name just a few, are all facing their own slowly unspooling financial disasters.

The blame lies with what economists call “deferred costs.” Generous pension promises made decades ago, without enough funding, are now coming due as baby boomers retire. Bonds issued in the distant past to build bridges, highways and other projects also must be paid — even as the projects themselves could by now use expensive makeovers.

You cannot necessarily see deferred costs, lurking in a shadowy realm known as “off the balance sheet.” But deferring them doesn’t make them go away. They actually compound.

“New York City has $85 billion of retiree health obligations all by itself,” said Richard Ravitch, the former lieutenant governor of New York State and an informal adviser to Detroit’s financial control board. He helped New York City resolve its financial crisis in 1975; today he worries about possible replays across America.