There was plenty of evidence prior to the invasion that Iraq did not have weapons of mass destruction, or that if they did they would be almost unusable because

There was plenty of evidence prior to the invasion that Iraq did not have weapons of mass destruction, or that if they did they would be almost unusable because of age. Information about this came out not only through organizations like the FAS (you may not have read about this in the NYTimes, but don't blame the opponents of the war for this), public statements by diplomats and civil servants (i.e. David Miller), the pressure to recall UN investigators (who were skeptical of the existence of such weapons), and evidence of deliberate fraud in pushing for war as in the yellowcake uranium setup, Colin Powell's presentation to the United Nations on "mobile weapons factories", or Dick Cheney's efforts to take control of intelligence work when the results were skeptical of his claims that WMD existed. The only actual evidence in favor of the hypothesis that Iraq might have WMD was that the country had not accounted to the UN investigators for the disposal of some dual-use chemicals the United States had sold them during the Iran-Iraq war. They claimed these materials were already destroyed and so could not document their destruction, which seems - in retrospect - to have been the case. Either way, if I remember correctly, these materials would have been almost if not totally unusable given their age.