Gene Epstein of Barron’s laments the major-party presidential candidates’ inattention to a major fiscal problem.

If the next U.S. President is Hillary Clinton, her first act in office should be to ponder key statements made by her husband and President Barack Obama on the demographically fueled debt crisis. Donald Trump could also benefit from their insights.

In his 1999 State of the Union address, President Bill Clinton warned, “With the number of elderly Americans set to double by 2030, the baby boom will become a senior boom,” leaving the government “unable to pay the full benefits older Americans have been promised.” Obama echoed these concerns in his 2010 State of the Union speech, observing, “We…still face the massive deficit we had when I took office. More importantly, the cost of Medicare, Medicaid, and Social Security will continue to skyrocket….Let’s invest in our people without leaving them a mountain of debt.” …

… I cite Clinton and Obama mainly to show that it isn’t just the nonpartisan Congressional Budget Office that has sounded the alarm about the crushing debt burden. The reality is hard to ignore, but that’s what the two main presidential candidates are doing.

U.S. Treasury debt held by the public has leaped from 38.4% of gross domestic product in 1999 to 76% in 2016. Now, if nothing is done, the CBO projects that the share could soar to 141% by 2046—way above its World War II high of 113% and still climbing. (See the CBO’s “2016 Long-Term Budget Outlook,” July 12.) The agency has argued repeatedly that the soaring debt could spark a fiscal crisis.

Skeptics might wonder how it is possible to predict fiscal red ink over more than a quarter-century, when it’s hard enough to forecast what will happen next year. The CBO’s prediction is only an attempt to make vivid the real point: Given three underlying factors, the dangers of out-of-control debt are too plausible to be ignored.

The main factor, as Bill Clinton pointed out 17 years ago, is demographic: “The baby boom will become a senior boom.” …

… The second factor, by the CBO’s reckoning, is that the per capita costs of health care keep rising faster than GDP, which will especially ramp up the cost of Medicare. …

… The third factor: Today’s unusually low interest rates, which make it relatively cheap to service the debt, aren’t likely to last. For example, the CBO predicts the 10-year Treasury rate, now below 2%, could hit 4% over the next decade, which is still well below the average of 5.8% from 1990 to 2007. As this occurs, a vicious cycle will take hold, with rising costs of servicing the debt making it necessary to borrow even more.