... I get a little queasy when I hear Democrats talk about Iraq teaching lessons about the need for solid intelligence. The lessons I've learned about Iraq go to the strategic calculus that says "we should engage in unilateral preventive military strikes to prevent countries from acquiring nuclear weapons in order to bolster US hegemony in the Persian Gulf," not a lesson about how one should or shouldn't process internal Intelligence Community disagreement about the state of a foreign WMD program.
An important point about Cheney, regardless of what you think about his motivations, is that he could have been right. In this particular case, U.S. intelligence overestimated Saddam's nuclear capacities; in other recent cases, though - Iraq circa 1991, Pakistan in the late-1990s - the same intelligence system significantly underestimated a foreign country's capacity to produce a nuclear weapon. In other words, sometimes a Dick Cheney approach to analyzing intelligence - the assumption that things are worse than the CIA says they are, rather than better - will turn out to be correct. Which is why it isn't enough to boil the Iraq debate down to an argument over spycraft and the interpretation of ambiguous data; you then have to abstract from what the intelligence says to what we should do about it, and the lessons of the Iraq occupation - to my mind, at least - tend to militate against a strategy of military preemption/prevention even in cases where an invasion would prove the Dick Cheneys of the world right.
That said, Matt Feeney's point about process is also a good one:
... the more relevant question is not about veracity or intentions. It’s about process: the disastrous combination a very popular administration pressing extreme constitutional prerogatives, a rollover Congress ceding its oversight authority (and it’s own war making power) on the eve of war, and a superhumanly willful Vice President using the most awesome bureaucratic ninja skillz in the history of bureaucracy to exploit the constitutional ambiguity of his office and push highly idiosyncratic policies through highly unconventional (and conveniently direct) paths to the President’s desk. Who was lying is almost a moot point. People become irrationally, existentially attached to ideas they have to fight and hurry and scheme to implement but don’t have to defend in open argument. This seems to be an obvious risk in having a unitary executive jealously guarding its commander-in-chief authority.
Also, for an interesting treatment of the broader topic of why we went to war and how the WMD analysis factored in, I recommend my friend Elbridge Colby's recent essay on George Tenet, particularly the later sections of the piece.