Media reports in recent weeks say that Senate Democrats are considering a 3% surtax on income over $1 million to raise federal revenues. This would come on top of the higher income tax rates that President Obama has already proposed through the cancellation of the Bush era tax-rate reductions.

If the Democrats' millionaire surtax were to happen—and were added to other tax increases already enacted last year and other leading tax hike ideas on the table this year—this could leave the U.S. with a combined federal and state...