1. al-Qaeda leadership fled Afghanistan for Pakistan before the US invasion, and the US knew it but invaded Afghanistan anyway.

2. Saddam Hussein's chemical weapons were well known to America, because American intelligence helped him acquire and target those chemical weapons against Iran in the Iraq-Iran War. Even going so far as to provide him with satellite intelligence for this purpose.

3. The "WMDs" used to justify the invasion of Iraq to the public were not chemical gasses. The US government claimed Iraq had a nuclear weapons program in advanced stages of development. This was never true and they knew it.