"If, say, a US adversary creates a great-looking video of the US president doing/saying something really heinous (...)" Did we not see enough fake stories about US presidents already? The DeepFakes are not really needed to falsely accuse a politician, or to wash away the compromising material. The media can use anonymous sources to claim anything bad about any public figure without consequences. Also, they can ignore and diminish any compromising material, effectively shielding the subject. It is all about who controls the media and subsequently the narrative. DeepFake may or may not be used in court though.