As the battle over Medicaid expansion rages in the states, supporters of expansion have dusted off an age-old favorite in making the case for taking federal dollars. They say: If our state doesn't take the money, those dollars will go to some other state instead.

Happily, in this instance that is not true. When a state declines to expand Medicaid coverage to more people, no other state will receive its share of funds and federal spending declines. Based on figures from the Congressional Budget Office and analysis by the Kaiser...