There are plenty of brilliant Nobel prize laureates who make elementary mistakes on a regular basis. Tyler Cowen and Milton Friedman to name two. So it's not in

There are plenty of brilliant Nobel prize laureates who make elementary mistakes on a regular basis. Tyler Cowen and Milton Friedman to name two. So it's not inconceivable that Krugman made a basic mistake here. (He didn't in this case, but not because he's too smart to make mistakes.)