I don't see Trump's speech patterns as a sign of mental decline. I see them as a sign that he's boxed himself in. In this interview, he's still open to ideas and searching for solutions. Now, six years later, he's got half a dozen or so radical solutions to defend, and the "soundbite" nature of political campaign coverage means that he can't give detailed explanations every time they come up. So we get shortcuts. "Everybody knows" is one of them.