When he was campaigning for office four years ago, President Joe Biden promised to be “a bridge” to the next generation of leaders. That bridge will be four years shorter than Biden may have planned. Biden, the oldest president in American history at age 81, announced Sunday that he will not seek reelection this year. The announcement ends weeks of speculation about the future of Biden’s campaign—and it could kick off a mad scramble to replace Biden on the top of the ticket, with the Democratic National Convention (DNC) approaching quickly and the general election less than four months away. “…