Soaking the rich is good politics but bad economics. Millions of Americans are beginning to see the fruits of the federal tax overhaul passed in December, with higher take-home pay, bonuses, and a stronger job market. However, these good times could soon end in some left-leaning states that are considering raising their income taxes. New Jersey, Massachusetts, and Maine may soon place surtaxes on “millionaires,” via legislation in the Garden State and ballot measures in the others. To proponents of larger government and greater state-level redistribution, raising rates on “fat cats” is a perfect way to fund more Medicaid and...