Graham Platner’s most vocal supporters are doubling down. There was a moment earlier this week — after Maine Gov. Janet Mills announced her candidacy for Senate; after a tranche of old Reddit posts triggered debate over Platner’s views on everything from gun rights to racial stereotypes; and, most crucially, after video emerged of him dancing in his underwear and showing off the solid dark Nazi Totenkopf tattoo on his chest — when it looked like the populist, oyster-shucking, anti-genocide veteran’s attempt to take down Republican Sen. Susan Collins would be over before it had really even started. Then new polling...