UAW President Shawn Fain, left, clasps hands with President Biden after endorsing his bid for reelection.Saul Loeb/AFP via Getty Images Marick Masters, Wayne State University The United Auto Workers has endorsed President Joe Biden’s bid for reelection in 2024. “Joe Biden has earned it,” said union president Shawn Fain on Jan. 24 as he announced the union’s decision to back the incumbent candidate. The Conversation U.S. asked Marick Masters, a Wayne State University scholar of labor, politics and business issues, to explain why the UAW waited until now to endorse Biden and why this endorsement…