Krugman's 'credibility' was based on his work in economics. Based on what he wrote about the President's social security plan last Friday, it seems either he isn't very good at distinguishing between opportunity cost and a loan or he does and doesn't really care about anything resembling the truth.
Even worse, after the National Review Online caught his egregious errors (link in title) he failed to print a correction in the NYT, rather he put a self-serving post on the left wing blog "Atrios" signed PK.
"My column this morning wasn't the finest - sometimes the magic works, sometimes it doesn't."
Magic? How about fact? What I'd like to see is the Krugman Truth Squad go back through Krugman's earlier work with a fine-toothed comb to see if there are any inaccuracies there.