To see why Giuliani’s interviews are only sane if Trump is planning a “so what” defense, consider how damaging the revelations are to the alternate defense that Trump was seeking to fight corruption, not achieve personal gain.
Most basically, Giuliani’s narrative shows definitively that Ukraine policy was being driven by Trump’s personal political objectives, not by the national interest. That’s why Giuliani, a man with no U.S. government position — but with a direct, personal attorney-client relationship with the president — was driving the policy. It’s not normal for the president’s personal attorney to advise on the removal of an ambassador — who doesn’t work for the president personally, but for the U.S. government. The very fact of Giuliani’s advice, coupled with its ultimate success, helps prove the case that Trump was abusing his office, using the power of the presidency to advance his personal goals.
Put another way, Giuliani’s interviews connect the dots between the policy of seeking the investigations from Ukraine and the president’s personal goal of reelection. If the investigations had been aimed at rooting out corruption, it would have been logical for the State Department or the Justice Department to seek and demand them. Astonishingly, Giuliani seems to be going out of his way to make the very case that the House Democrats tried to make in the hearings before the intelligence committee: that Giuliani was the tool through which the president subverted the national interest to his personal advantage.