There are numerous contrasting examples from decades ago, including this — with sophisticated grammar and syntax, and a coherent paragraph-length chain of thought — from a 1992 Charlie Rose interview: “Ross Perot, he made some monumental mistakes. Had he not dropped out of the election, had he not made the gaffes about the watch dogs and the guard dogs, if he didn’t have three or four bad days — and they were real bad days — he could have convincingly won this crazy election.”
The change in linguistic facility could be strategic; maybe Trump thinks his supporters like to hear him speak simply and with more passion than proper syntax. “He may be using it as a strategy to appeal to certain types of people,” said Michaelis. But linguistic decline is also obvious in two interviews with David Letterman, in 1988 and 2013, presumably with much the same kind of audience. In the first, Trump threw around words such as “aesthetically” and “precarious,” and used long, complex sentences. In the second, he used simpler speech patterns, few polysyllabic words, and noticeably more fillers such as “uh” and “I mean.”
The reason linguistic and cognitive decline often go hand in hand, studies show, is that fluency reflects the performance of the brain’s prefrontal cortex, the seat of higher-order cognitive functions such as working memory, judgment, understanding, and planning, as well as the temporal lobe, which searches for and retrieves the right words from memory. Neurologists therefore use tests of verbal fluency, and especially how it has changed over time, to assess cognitive status.
Maybe he even used to know what the nuclear triad was, or how many articles the Constitution has.
[Update a few minutes later]
Related, I think: What a conservative sees from inside Trump’s Washington:
for connected conservatives in DC, the media isn’t the only source of information about this administration. I’d venture to say that most of them have by now heard at least one or two amazing stories attesting to the emerging conventional wisdom: that the president either can’t, or refuses to, follow any kind of policy discussion for more than a few minutes; that the president will not be told no, or corrected about anything, forcing his staff to take their concerns to the media if they want to get his attention; that the infighting within the West Wing is unprecedentedly vicious, and that those sort of failures always stem from the top; and that his own hand-picked staffers “have no respect for him, indeed they seem to palpitate with contempt for him.” They hear these things from conservatives, including people who were Trump supporters or at least, Trump-neutral. They know these folks. They know, to their sorrow, that these people are telling the truth.
They can also compare what they’re hearing to what they heard, both on and off the record, during the last Republican administration. Even in Bush’s final days, when the financial crisis was in full swing and his approval ratings hovered around 25 percent, there was nothing like this level of dysfunction inside the White House, this frenzy of backbiting leakage.
So even though they agree with conservative outsiders that the media skews very liberal, and take all its pronouncements about Republicans with a heavy sprinkling of salt, they know that the reports of this administration’s dysfunction aren’t all media hype. They have seen the media report on their own work, and that of their friends; they know what sort of things that bias distorts, and what it doesn’t. Washington conservatives know that reporters are not making up these incredible quotes, or relying only on Democratic holdovers, or getting bits of gossip from the janitor. They know that the Trump administration is in fact leaking like a rusty sieve — from the top on down — and that this is a sign of a president who has, in just four short months, completely lost control over his own hand-picked staff. Which is why the entire city, left to right, is watching the unfolding drama with mouth agape and heads shaking.
This is why people are seriously talking about the 25th Amendment.
[Update a few minutes later]
Seriously, this should concern Trump supporters who want him to “drain the swamp”: