Let’s imagine that Franklin D. Roosevelt had possessed the same gift for longevity as Jimmy Carter and lived until he was 100. He would have died in1982, in Ronald Reagan’s second year in office.

Jimmy Carter redefined his legacy after his presidency. Other presidents, especially Hoover and Nixon, tried but failed to outrun or outwork their unhappy presidential legacies. Like John Quincy Adams before him, Carter will mostly be remembered for what came after his time in the White House rather than those four years in it—as he should be.

A national day of mourning is a day to honor and pay respects to a revered public figure who has died. Here's what else to know.

Jimmy Carter and Demetrius Young both died Dec. 29. The two men shared a life of service, a love of Georgia, and a care for the needs of everyday people.