In 1979, a junior diplomat at the State Department named John Graham negotiated a deal with Cuba whereby Castro would use his good relationship with Iran to get the American hostages freed.
Graham tells the fascinating story here. (Full disclosure: Graham is a personal friend, but he has never suggested that I promote his writings.)
Graham's deal was a nonstarter due to the State Department's idiotic Cuba policy, but if it had been allowed to go forward, Jimmy Carter would surely have been re-elected in 1980, and had Reagan tried to run again in 1984 he would no doubt have been dismissed as too old.
Imagine: no Reagan. The mind reels.