I thought that Bush considered Kerry's remarks so self-defeating on their face that he was afraid to push back too hard. Bush's theme was that Kerry just simply didn't have a grasp on the reality of geopolitics...he was rearing to respond to the inanity at every chance. It was like a President debating a 7th grader on how to conduct foreign policy. The 7th grader has no concept of the stakes, the nature of the players and the negotiations, and has no feel for where his fantasies and and reality begins.
Plainly stated, the proper response would be, 'Are you friggin kidding me Senator? -- this is some of the most dangerous and idiotic shit I've ever heard in my life.'
I think that was going through Bush's mind, and he tried to be forceful but was aware he might step over a line if he wasn't careful. Kerry was just too goofy to be taken head-on....we all know the dangers of getting into a point-by-point argument with an idiot...it can just bog you down. Kerry made too many gaffes to deal with them all one by one and still get a message across, so Bush tried to stay on message and keep it simple.
I thought he did make Kerry look small and unrealistic, and he made some bunker-busting responses, and dropped heavy nukes at the end in the closing remarks.
Bush was very effective in my eyes.