Four years ago, candidate Joe Biden stood before supporters at a Detroit high school, flanked by Kamala Harris and other rising Democratic stars, and called himself a bridge to the next generation of leaders. Biden, now a president seeking reelection, returns to the city Friday with many in his party now pleading for him to fulfill that very promise and step aside. During a news conference on Thursday, when asked why he no longer considered himself a “bridge” to the next generation of leaders, Biden responded that “what changed was the gravity of the situation I inherited in terms of the economy, foreign policy, and domestic division."