Marine veteran Graham Platner was nominated by Maine Democrats on Tuesday to face Republican incumbent Sen. Susan Collins in November’s midterm elections. Although Platner’s 72% victory was a landslide among Democratic voters, nearly 1 in 5 voters still picked Janet Mills, the current governor of Maine, who had stopped campaigning in April after struggling to raise enough funds. Given the scandals that have plagued Platner, the 41-year-old oyster farmer, some have wondered: Is his victory emblematic of a larger willingness among Democrats to overlook ethical questions among their nominees, much like they’ve criticized Republicans for doing over the last decade?...