For the first time in generations, a milestone in the federal debt-to-GDP ratio has arrived that most economists hoped never to see again, and the forces that drove it there make it nearly impossible to reverse.

Debt held by the public hit 100% of gross domestic product for the fiscal year that ended Sept. 30. The Wall Street Journal reported Thursday that this is the first time the ratio has reached triple digits since 1946. Harry Truman was president in 1946, so President Trump is the first president since Truman to see the fiscal-year ratio this high. That comparison marks the date and places no blame. The Journal links the debt to decades of tax cuts, emergency spending and an aging population under both parties.

The Journal said the government reported $32.2 trillion in publicly held debt as of Sept. 30. Measured against GDP for the fiscal year, using the third-quarter figures released Thursday, that came to 100.03%, just over the line.…