The Democratic Party is at war with itself — and in Maine, the fight has spilled into the open. Graham Platner, an alleged rapist with a Nazi tattoo on his chest, won the Democratic nomination for United States Senate last month, beating the candidate the party establishment had recruited by a commanding 53-point margin. For months, Republicans and others had warned that Platner was unfit for the job. The Democrats did not care. As soon as party leaders saw polling that suggested he could beat Republican Sen. Susan Collins in November they embraced him, hosting him in Washington, DC, and pledging as...