Oliver North selling weapons to Iran in order to fund an illegal war in Nicaragua. At the time it was huge, the idea that someone with the rank of lieutenant colonel could sell arms to a declared enemy was, in and if itself, an outrageous scandal. That he did so with the intention of using the funds to support a war that congress had explicitly defunded was even more scandalous. That he was convicted and only got probation - I don't think our country has ever recovered. It proved that certain military and intelligence officials were above the law, above even congress and the president.
I'd be shocked if more than 1% of people under 30 know this even happened.