Giuliani’s defense will likely be that he was acting completely at Trump’s direction and that his efforts on behalf of the officials and oligarchs was done to curry favor with them on Trump’s behalf, and was done at Trump’s behest and his knowledge. Purely from a perspective of trial strategy, Giuliani’s best defense would include testimony from the former president that he knew everything Giuliani was doing and approved of every action he took. That would permit Giuliani’s defense team to argue that since he was ultimately advancing Trump’s interests, he was actually working on behalf of the United States, not Ukrainian oligarchs. Unfortunately for Giuliani, Trump is not known for sticking his neck out for disgraced former aides, particularly if doing so would involve personal embarrassment or potential liability. Given how Trump distanced himself from former lawyer Michael Cohen when he faced similar peril, it is hard to imagine the former president taking an oath to tell the truth and subjecting himself to withering cross-examination that could embarrass him at best or expose him to potential liability at worst. (Trump’s record of lying under oath in civil suit depositions is well documented.) The only surefire way for Trump to avoid testimony in the trial of Giuliani would be to take the Fifth, but Trump has repeatedly noted that taking the Fifth makes you look guilty. The only way for him to get out of testifying is for him to suggest that he didn’t really know what Giuliani was doing and didn’t approve of his activities. That would make him worthless for Giuliani as a witness and force Giuliani to point the finger at Trump to save himself.