PORTLAND, Maine — Former Democratic Senate nominee Graham Platner is no longer set to speak at a Labor Day rally when he makes his first major public appearance since ending his campaign against Republican Sen. Susan Collins of Maine.Platner, who won the nomination in June but dropped out in July after Politico reported that a former girlfriend said he sexually assaulted her, had been scheduled to speak Monday at the rally in Ellsworth, near his hometown of Sullivan. He has denied the allegations.Platner was expected to speak about labor history and the importance of unions in the U.S. Event organizers...