Sorry for the earlier, semi-sarcastic post. My anti-Beltway bias blinded me to the fact that several Cato people did oppose the Iraq invasion before the fact, e.g. here. Brink Lindsey's famous defense of pro-war libertarianism (e.g. here) stuck out in my mind, but that's not Cato's fault; obviously the WSJ would promote views it agrees with.
So sorry Cato. I had erroneously remembered only the Mises Institute and Independent Institute publicly opposing the invasion.