Bush was unwilling to trust the U.N. inspectors. The CIA had also thought that there were no weapons. Bush took this as evidence that Saddam was hiding weapons. Literally, on 9/12, Paul Wolfowitz asked for intelligence that Saddam had WMD and there wasn't any. With so much pressure from the top to find evidence for WMD, the CIA started to cave.
(Saddam had incentive to pretend he had WMD. He certainly didn't want Iran to know he didn't. He obviously didn't want inspectors inside his government buildings. But Bush and his team used Saddam's behavior as evidence he was hiding WMD, rather than the fact that he was hiding the lack of WMD.)
Once the CIA realized that war was inevitable, it went into cover-your-ass-mode and said Saddam might have chemical weapons so that US soldiers wouldn't go into Iraq with insufficient protection in-case there were chemical weapons after all.
Bush was unwilling to listen to counter-naratives. If Condi Rice or, more likely, Colin Powell had been willing to say "I don't think war is such a good idea" maybe it wouldn't have happened. But Bush surrounded himself with yes men. If Powell hadn't supported the war, likely he and his entire staff would have had to resign. If that had happened, Bush would have lost Tony Blair's support and with that, any international support. Bush probably would have at least thought twice about going to Iraq alone.
So in this case, it wasn't so much that the institutions weren't trustworthy, it's that they fell in line with pressure that started from Bush. It doesn't do any good to have experts at your disposal if you're not going to listen to any of them.
Source: Robert Draper's exhaustively researched book on how Iraq happened:
(Also, the U.S. media didn't do its job. The cynical side of me says there's money to be made in covering war. But probably, it was just incompetence. I still haven't forgiven the NYT though.)
(Saddam had incentive to pretend he had WMD. He certainly didn't want Iran to know he didn't. He obviously didn't want inspectors inside his government buildings. But Bush and his team used Saddam's behavior as evidence he was hiding WMD, rather than the fact that he was hiding the lack of WMD.)
Once the CIA realized that war was inevitable, it went into cover-your-ass-mode and said Saddam might have chemical weapons so that US soldiers wouldn't go into Iraq with insufficient protection in-case there were chemical weapons after all.
Bush was unwilling to listen to counter-naratives. If Condi Rice or, more likely, Colin Powell had been willing to say "I don't think war is such a good idea" maybe it wouldn't have happened. But Bush surrounded himself with yes men. If Powell hadn't supported the war, likely he and his entire staff would have had to resign. If that had happened, Bush would have lost Tony Blair's support and with that, any international support. Bush probably would have at least thought twice about going to Iraq alone.
So in this case, it wasn't so much that the institutions weren't trustworthy, it's that they fell in line with pressure that started from Bush. It doesn't do any good to have experts at your disposal if you're not going to listen to any of them.
Source: Robert Draper's exhaustively researched book on how Iraq happened:
https://www.amazon.com/Start-War-Bush-Administration-America...
Interview with the author:
https://www.vox.com/2020/9/2/21417224/why-did-america-invade...
(Also, the U.S. media didn't do its job. The cynical side of me says there's money to be made in covering war. But probably, it was just incompetence. I still haven't forgiven the NYT though.)