The way people react when they're not prepared or stunned or momentarily out of it is common -- maybe even universal.
Remember Rick Perry in the 2012 debates.
I remember one candidate for lesser office falling eerily silent in a debate a few years's back as well.
Being glib and having something to say -- no matter how inane -- about everything is also (sadly) human.
Being at one extreme and not seeing humanity on the other is what's not all that "human."
My personal favorite was the debate between Gore, Quayle and Stockdale. Gore and Quayle were going back and forth, then the host called a halt so Stockdale could get a word in and his comment was, 'I'm out of ammunition on this one,' and then Gore and Quayle went right back at it.