MIAMI — With about 10 police officers standing behind him, U.S. Sen. Marco Rubio was endorsed Saturday by the state’s main police union, the Florida Police Benevolent Association, a group that represents about 30,000 cops statewide. It is the latest law enforcement group to back him in his reelection campaign — including endorsements from a group of 55 Florida sheriffs and the Florida Police Chiefs Association — against U.S. Rep. Val Demings. Demings, a Democrat and the former Orlando police chief, has made efforts to emphasize her law enforcement background, rebuking the movement to defund th…