When he "stammers" as you say...he is thinking and trying to say AGAIN in another way to say what he said probably two questions ago.
Unlike the former occupant of the White House, who could glibly ad lib 12 lies a minute in 6 languages (or was that accents?) at the drop of a hat, only to be admired by an adoring press, which wondered in awe 'how'd he do that'?