. >> reporter: economics professor alan blinder, a past vice chairman of the fed, hired ben bernanke at princeton, so of course he's biased. but in his post-crash bestseller, after the music stopped, even blinder takes bernanke to task for letting lehman brothers fail, freezing credit worldwide. that lowers the grade from a straight a or a+. >> the lehman episode just sticks in my craw, not to save lehman or put them to bed in a more gentle way, this is a joint mistake of ben bernanke and hank paulson, who was secretary of the treasury, but it was very consequential. i mean as you know, all hell broke loose the very next day. >> reporter: but at a town hall in 2009, bernanke told jim lehrer that the fed didn't have the legal authority to intervene in an investment bank like lehman. >> in the case of lehman brothers, there was just a huge $40, $50 billion hole that we had no way to fill and no money, no authorization, no way to do it, so we had to let it fail. we had no choice. >> reporter: to blinder, though, the government made up all sorts of tools during the crash. >> guess what?