Speaking of damaging, severely dirty campaign tricks, we should talk about the egregious lie that Jerry Falwell spread in speeches all over the country and on TV ads. Although this dirty trick was not as damaging as Casey's October Surprise deal with the Iranians, it did great damage.
Falwell claimed that in a White House meeting Carter told him he had to have gays on his staff because gays in the U.S. needed representation on his staff. Falwell made this false claim to audiences all over the country. When confronted with a recording of the meeting that proved Carter said no such thing, Falwell admitted he had fabricated the story. Yet, Falwell then helped fund a TV ad that showed a concerned mother telling her child that Carter was a bad man because he encouraged homosexuality.
This lie did great damage to Carter's support among evangelical Christians, a voting block that he had won handily in 1976. The sizable drop in evangelical support cost Carter the states of Mississippi, Alabama, South Carolina, Arkansas, Tennessee, and Kentucky, where he lost by razor-thin margins.