Trump cannot ever keep his story straight because he never fully knew what it was in the first place. He knows it is about him, and the things that keep happening to him, but beyond that he never knows, and will never know; he is conspiring and scheming constantly, but so ineffectually and in such a state of flummoxed confusion and utterly abject ignorance that the endgame is never anything but unclear.
When the White House released a redacted summary of a phone call that Trump had with Ukraine’s newly elected prime minister—this, oddly, was part of a confusing attempt to short-circuit a scandal that began with the White House’s attempt to bury a whistleblower’s complaint about Trump’s attempt to cultivate foreign parties’ help in his 2020 campaign—the world got to see the master in action. The dialogue made clear what Trump was trying to do, which was leverage the possibility of aid money to get Ukraine to investigate a company that had put Joe Biden’s son Hunter on its board, thereby creating the sort of opaque and open-ended scandal that Trump used to great effect against Hillary Clinton in 2016. It was the transparency of this maneuver—which, in classic Trumpian fashion, amounted to making a common bit of implicit political scummery extremely explicit, and then using it to the pettiest of personal ends—as much as the substance of it that seems finally to have inspired Democrats to come around on a shamefully belated impeachment inquiry.
Trump’s ignorance isn’t a defense, but it is again a decent explanation. Because he is constitutionally incapable of being less ignorant—because his mind is gone and because he won’t read or listen and can’t effectively digest even the smoothest gruel that his television gives him—he winds up thinking things that literally no one else thinks. And because Trump is constitutionally incapable of changing his mind, on any topic, he gets stuck on stuff like this and then repeats it and repeats it and repeats it; the job of the cable channel he likes is to tell him he’s right, so quite literally hears this stuff more and more. He doesn’t express himself well enough to convince anyone else of whatever it is that he believes—it’s seldom clear what he’s even trying to argue beyond that everyone is being mean to him for no reason and actually someone else did what he did—but he’s already convinced himself of it, which means that he will never be unconvinced.