Krugman gets a bit snippy at 48:20. His objection is confused. He says Professor Schwartz tried to criticize his credentials. But Schwartz criticized Krugman for going beyond his capabilities, not for going beyond his credentials.
Schwartz makes a strong point about the "ratchet effect" in government policy at 1:09:00. He credits "ratchet effect" studies to the Public Choice school, although of course, it's mainly an insight of Robert Higgs', who isn't usually classed as a Public Choice economist.