I also recommend reading Ta-Nehisi Coates' response, partially reprinted here:
Ross's point that he can't imagine himself doing anything different than Truman, doesn't really exonerate Truman, basically because neither Ross--nor I--would ever be president. I'd argue that a leaders are not simply supposed to be carbon-copy representatives of our emotions, but that they're supposed to see more, they are supposed to be better than. Asking ourselves what we would do, were we in Bush's shoes is likely to only prove that we'd be very mediocre presidents.
Much stronger is Ross's point that basically anyone other potential president in Truman's shoes would have done the same thing as Truman. But you simply can't make the same argument about Bush. Indeed, it's not even clear that every potential Republican president would have approved of water-boarding.