For better or worse, a truism of American politics is that voters vote their pocketbooks. Yet according to a new report on median household incomes by Sentier Research, in 2012 millions of American voters apparently cast ballots contrary to their economic self-interest.

Each month the consultants at Sentier analyze the numbers from the Census Bureau's Current Population Survey and estimate the trend in median annual household income adjusted for inflation. On Aug. 21, Sentier released "Household Income on the Fourth Anniversary...