Robert J. Samuelson [“The real U.S. debt picture,” op-ed, Feb. 25] is right to focus on the size of the national debt under any of his five scenarios. However, it is also important to consider the potential impact on the annual deficit of interest rates ticking up from their current, artificially suppressed levels. Using Mr. Samuelson’s baseline figure of an $11.3 trillion debt level, a 1-percentage-point increase in the average interest rate paid on this debt would produce $113 billion more in annual interest expense. Greater increases in the average rate would boost the annual deficit even more dramatically.

Tad Howard, Potomac