ATLANTA- Missouri Democrat Jason Kander spent this week knocking on voters’ doors, shaking hands, giving speeches and snapping selfies with eager young campaign volunteers. In Georgia. He was in Atlanta on the last leg of a cross-country tour, the sort that tells the political cognoscenti that this is an up-and-comer to be watched closely. But this is a guy who’s never held an office higher than secretary of state in Missouri. He narrowly lost a winnable Senate campaign last year. He currently holds no political office, and the Kander Political Action Committee is dormant. He says he’s dedicated to his...