Will the Fed hit its inflation target by 2025? Don’t bet on it.

Earlier this week, Treasury Secretary Janet Yellen made headlines when she expressed optimism that the Federal Reserve Board’s long hoped-for 2 percent inflation target might be achieved by 2025. The attention was understandable.

For one thing, when inflation reaches the target, we can expect lower interest rates and more economic normalcy. For another, at the time, the most recent readings on the all-item Consumer Price Index still showed May year-over-year inflation running 3.3 percent...