Donald Trump is losing his words. His vocabulary is significantly less rich than it was a decade ago, and his speech pattern resembles that of a child. He is even losing common words. When complaining about how he is treated by the press, he said "No politician in history, and I say this with great... surety... has ever been treated worse or more unfairly."
The statement is of course ridiculous. Plenty of politicians in history have been imprisoned, tortured and killed, and US presidents have been assassinated, which is definitely worse than being called out in the press for being a liar. However, his inability to find the right word is a lot more important here. Forgetting the common word "certainty" or "confidence" is a deeply troubling sign of dementia. A normal person with a clear mind just doesn't talk like that.
Donald Trump needs to have his head examined.
