Sen. Bernie Sanders's rise, his supporters, and the national mood he is running in mirror the president's circumstances four years ago, and the primary is an early tell. Bernie Sanders has the lead in the Democratic primary and, while far from over, his supporters’ enthusiasm greatly outpaces any of the rival campaigns and he is poised to continue winning contests and delegates. Party leaders and a good deal of their supporters in the media are in a full panic, struggling to derail the socialist insurgent’s campaign before he leads the party to what they predict is electoral ruin and four...