If he had choosen to say, "Yes, there were some things we did wrong. I wish our actions had not so distanced us from our allies. But it was still the right choice at the time." He could have mended fences. In one fell swoop he could have won over moderates, undecides, and maybe even some democrats.
I want a President who will to listen to all the people in this country. I want a President who is willing to examine his actions, and if he makes a mistake, to own up to it. After all, you can do something for all the right reasons and still have it turn out to be a mistake. That's what hindsight is for.