Some American disasters come as bolts from the blue — the stock market crash of October 1929, Pearl Harbor, the designated hitter, 9/11. Others are predictable because they arise from arithmetic that is neither hidden nor arcane. Now comes the tsunami of pension problems that will wash over many cities and states.

Dallas has the fastest-growing economy of America’s 13 largest cities but in spite of its glistening commercial towers it represents the skull beneath the skin of American prosperity. According to its mayor, the city is “walking into the fan blades” of pension promises: The fund for retired police and firefighters is $5 billion underfunded. Prompted by projections that the fund will be exhausted within 20 years, retirees last year withdrew $230 million from it in a six-week span. In the entire year, the fund paid out $283 million and the city put in just $115 million. In November, the New York Times reported that the police and fire fund sought a $1.1 billion infusion, a sum “roughly equal to Dallas’s entire general fund budget but not even close to what the pension fund needs to be fully funded.”

Nowadays, America’s most persistent public dishonesties are the wildly optimistic but politically convenient expectations for returns on pension fund investments.