If that dynamic holds, Platner, a political newcomer and reformed bad boy who favors jeans, flannel, and the F-word, could be headed to a primary victory in June as the scruffy new face of Democratic politics. Despite an online history that includes dismissive comments about rape, homophobic slurs, and other insults, progressive Democrats like Senator Elizabeth Warren of Massachusetts are backing the 41-year-old Iraq war veteran. In the quest for youth and a fiery, populist message, all else is forgiven, including a Nazi tattoo that Platner has since covered up. Hoping to turn the tide, Mills has unleashed ads attacking...