I think at certain point they decided not to belabor the point because it was useless - the media and Democrats would simply keep repeating their "Big Lie" line.
Most normal people then were convinced that going in to remove Saddam was the right choice, as they have been before the invasion. The polls that may suggest that people now think removing Saddam and invading Iraq was not the right thing to do are usually a reflection of deliberately misleading poll questions and general disappointment and fatigue with "The Long War" that they hear "we are not winning", rather than any change of original opinion based on new "facts".
So Bush people likely decided that it's more important to convince people of importance of staying and "winning in Iraq" than to dwell on the reasons for going in. If things go well in Iraq, most people will be for going into Iraq in the first place, if things are still perceived as not going well, most people will say they are/were against invasion in Iraq. In other words, I think they decided to pick the battles they can win, and the PR battle will then (later?) take care of itself, based on situation in Iraq.
“I think at certain point they decided not to belabor the point because it was useless - the media and Democrats would simply keep repeating their “Big Lie” line.”
I think you may be right. I also think that was a huge blunder. By not having defended their credibility on the one hand they have lost it for all other such situations on the other. I would also argue that they were not only sacrificing their (the Bush administration’s) credibility, they sacrificed that of all Republicans, conservatives, you and me.
How can you govern when every time you attempt to do something our adversaries whip up the great whine — “How can we believe you when you were so wrong about Iraq?”