The New Yorker's Seymour Hersh gives us a rundown on why administration intel on Iraq was so bad. Listen to this from two sources, one from a CIA official, and the other being Ken Pollack, who supported the ouster of Saddam:

The point is not that the President and his senior aides were consciously lying. What was taking place was much more systematic—and potentially just as troublesome. Kenneth Pollack, a former National Security Council expert on Iraq, whose book “The Threatening Storm” generally supported the use of force to remove Saddam Hussein, told me that what the Bush people did was “dismantle the existing filtering process that for fifty years had been preventing the policymakers from getting bad information. They created stovepipes to get the information they wanted directly to the top leadership. Their position is that the professional bureaucracy is deliberately and maliciously keeping information from them.

“They always had information to back up their public claims, but it was often very bad information,” Pollack continued. “They were forcing the intelligence community to defend its good information and good analysis so aggressively that the intelligence analysts didn’t have the time or the energy to go after the bad information.”

The Administration eventually got its way, a former C.I.A. official said. “The analysts at the C.I.A. were beaten down defending their assessments. And they blame George Tenet”—the C.I.A. director—“for not protecting them. I’ve never seen a government like this.”

And what are these processes of "filtering" and "stovepiping"? From the article:

A retired C.I.A. officer described for me some of the questions that would normally arise in vetting: “Does dramatic information turned up by an overseas spy square with his access, or does it exceed his plausible reach? How does the agent behave? Is he on time for meetings?” The vetting process is especially important when one is dealing with foreign-agent reports—sensitive intelligence that can trigger profound policy decisions. In theory, no request for action should be taken directly to higher authorities—a process known as “stovepiping”—without the information on which it is based having been subjected to rigorous scrutiny.

There's plenty to read in the article, get to it.