WMD and Syria
It is now an article of faith for many people that Iraq had absolutely "no WMDs, and no connection with terrorism." I've posted numerous articles showing evidence that things were otherwise, including David Kay saying that lines of trucks that may have contained WMD left Iraq for Syria, and it's been like talking to a wall.
If they uncovered fifty nuclear-tipped missiles in the sands of Iraq, I can think of maybe two people here who would change their minds about the war. The rest would hiccup, and go on along another tack like nothing had happened.