I think he has core beliefs. They are based in racism, hate whitey, "Black Liberation Theology", radical Marxism, anti-capitalism, and anti-Americanism.
When he's teleprompter-less, it requires more effort than his limited intellect can muster to filter out the stuff that he knows would be political death to espouse. That's why we get the "uh, um, uh, and..." out of him.
He's trying his best to filter his beliefs so he doesn't say something stupid like "let's spread the wealth around, it's just neighborly".
Very good analysis. However, absorbing that is too much work for the average observer--even put as clearly and logically as you did. Fortunately, an accurate understanding of the reason for the uh uh uh uhs isn't necessary for the stammerings to have a negative effect. If people start turning from him because he comes off as incompetent boob without his teleprompter, that works too.