It is inexplicable as to why the White House ceded the offense to the anti-war crowd. Malkin mentions the important Podhoretz piece and Kevin Drum's response to its critics:
In the end, the story of the run-up to the Iraq war is about intelligence, but not in the way most people think. Intelligence is always flawed and imprecise, even more so when you're dealing with a closed, paranoid and authoritarian regime like Hussein's. It's foolish to suggest Bush should have bucked consensus estimates on Iraq WMD built from more than a decade of intel, and it's even worse to suggest he lied for not doing so.
What President Bush did instead was put an end to the decade-long guessing game and place the burden squarely on Saddam Hussein by saying in front of the world: "This is what we think you have. It's now your responsibility to prove us wrong." In the aftermath of the worst terrorist attack in the history of America, it was absolutely the right thing to do.
The main criticism that can be made of Bush is the trouble we've had with terrorists and insurgents after the fall of Iraq. We expected the people to embrace us immediately as liberators. That this assumption was wrong to the extent it was and how we had counted on this assumption in rebuilding Iraq is a very legitimate criticism.
However, this does not mean that the reasons for taking out Saddam were illegitimate. To attempt to rewrite history at this point, for political gain or because of some animus toward Bush, is a waste of time and energy and weakens us in the eyes of our enemy.
Update: Additionally, there were many reasons for invading Iraq with WMD being at the top of the list. However, the bigger picture is that this country can't play defense only against terrorism. We must eradicate terrorism where it thrives in the Middle East. How best to do this? Establish a democracy in Iraq.