“Or “uh”. He does that to distraction, and I’ve read that is a mark of lying (big shock). Hillary does that a lot too.”
It’s a neurolinguistic programming method that creates a gap where the listeners fill in what they anticipate the speaker will say, based on their own biases and personal interests. Everybody comes away thinking POTUS agrees with them.
It’s also a bad habit that pseudo-intellectuals use to sound more intelligent, as if they’re pausing to “gather their thoughts”. Jeff Goldblum does it a lot whenever he plays a scientist or intellectual. But you’ll never catch somebody like Chris Christie doing it, whether you like him or not, in public speaking his comments are always well-organized and he never has to pause for reflection.
Personally I also suspect the “uhhh” is used intentionally as a soothing tone like “ommm” which is meant to have a hypnotic effect on listeners.