The Iran-Contra Affair
This conspiracy rocked the Beltway when it came to light in the mid-1980s. Despite an arms embargo, the U.S. military was secretly selling missiles and other weapons to Iran, in hopes of getting seven American hostages released. If that weren't bad enough, the money from the illegal arms sales were diverted to the Contras, a guerilla group dedicated to overthrowing the government of Nicaragua. It was, incidentally, also prohibited for the U.S. government to fund the Contras.