Iran

A major mistake (but certainly not on the order of Bush's invasion of Iraq) in foreign policy occurred in 1979 when the inept President Jimmy Carter let Iran get away with an act of war. Hours after the Iranians invaded our embassy (considered our sovereign territory under long-standing international convention and/or law), Carter should have ordered our air force and navy to inflict heavy blows on Iran. Then, he should have gone on TV with an ultimatum to Khomeini: cease and desist your invasion of our embassy, and return our personnel unharmed, or else we will flatten your entire country.

Instead, Jimmy sent the following message to the world: "You can crap on us, and we won't do anything about it, because we don't want to kill innocent civilians." Well, Iran got that message, and later, so did Al Qaeda. In fact, that message got amplified over and over, as jihadis got off scott free after numerous attacks on Americans, culminating in 9/11.

As they say, you have to break eggs to make an omelet. In war, you have to break heads.