Once upon a time, the Republican Party was tearing itself apart. It was 1976, and Ronald Reagan was mounting a conservative challenge to the “accidental president,” Gerald Ford, for the GOP nomination. After a hard-fought primary and a convention fight, Reagan lost the nomination. But he won the Republican Party. And it was all sorted out at that year’s Republican National Convention.

In “The Contested Convention,” a short documentary directed by Stephanie Wang-Breal for FiveThirtyEight, we revisit the 1976 Republican primary, which set the GOP on a more conservative course for the next several decades.