That particular clip is also very telling, though not the "ugly face" one I thought I had seen. (still looking).
In yours, he is basically praising "colonialists" who came to America and wrote those amazing founding documents. We all know how he feels about colonialism, so I think the "uhhhhhh" was because after this particular positive use of colonialism struck him intellectually wrong, hence the "uhhhhhhh". He wanted to explain more or use another word, but it was too late, he had already said it. His speech writer boned him on that one.
I dunno. Maybe I'm reading too much in, but I try to pick up on small details of speech, facial expression, and body language sometimes. That's what I got out of that tiny little tidbit. I'll post the ugly face/colonialism tidbit if I find it.
Bagster