Over the years people on the right (including me) have enjoyed pointing out places where Krugman contradicts himself. He often responds by noting that people can and should change their minds when the facts change. Thus the famous Card and Krueger study on the minimum wage revised our view of that policy option. Or these new facts might be theoretical innovations, such as Krugman’s very own revisionist take on liquidity traps, from 1998. These are good arguments.