Krugman v. Krugman on Social Security:

Is Social Security in trouble? If you're talking to Paul Krugman, it would depend on when you asked him, as Ruth Marcus documents in this column. It's almost enough to make one think Krugman's become a crude partisan.

UPDATE: Krugman responds to Marcus here. Mark Thoma thinks Krugman has a good defense. Ramesh Ponnuru less so. And Henry Farrell is glad to see newspaper columnists engaging -- and actually challenging -- each other.