Overthrowing governments is awful foreign policy. This was never going to work, just like it didn't in Iraq, Iran, Vietnam, the Congo, Guatemala, Syria and elsewhere.
Here's the kicker: the invasion of Iraq was based on a convenient lie by hawks who had been keen to overthrow Saddam Hussein ever since the First Gulf War. This convenient lie was easily debunked to. It's really simple.
If Saddam Hussein had WMD, why wouldn't he give them up to save himself and his regime? Invasion clearly wasn't an empty threat and that would not end well for him. Hussein was never a religious ideologue. He didn't dream of martyrdom or jihad. He was a self-serving dictator (creates by the US I might add as a tool against Iran in the 1980s in a war that resulted from a revolution against the Shah, a government created by the US; are you beginning to see the pattern?). The only explanation was that Iraq did not in fact have WMDs.
People pointed out in the early days after 9/11 so this isn't some kind of historical revisionism. None of this ever made sense.