Well, everyone needs to realize that war is just that war. Nothing ever goes as planned during war. Mistakes will always be made. The final outcome however is what is important.
Yeah the one way for Bush et. al. to quell the growing voices of criticism is to admit the errors that were made, show that they are learning from them, etc. Everyone knows all bets are off once the war starts, so there can't be much valid criticism there. Denials and stonewalling the media/opposition just makes things worse.