A Sand-bagger is to Dems, what a Tea-bagger is to GOP; left wing-nuts who spend all their energy attacking Democratic leaders and organizations. Nobody in the party is as principled as they. They're blissfully unaware their gov't has a Congress, wherein bills are introduced, cycle through committee, are tabled or voted upon. They can't grasp that POTUS doesn't make laws; he signs or vetoes bills after they've passed Congress. They believe FDR passed reforms via a bully pulpit without 2/3 majorities of Dems in Congress. They were enthralled with Obama until they stayed home both mid-terms, and now blame Obama for the impact of their not voting. They believe the system is rigged against them, an irony, since the vast majority of them are white males. They think the DNC is a witch stirring the cauldron of all human suffering. Their confusion about the function of the DNC, comprised of 100s of party leaders and activists, causes them great angst, inspiring their ALL CAPS RANTS. Just like right wing blames the dysfunction in DC on the poor, POC, media, and gov't; the left wing blames the mess in DC on the rich, the DNC, POTUS, and the media. It's not enough for them to have one agree on the problems, also their solutions, no matter how implausible. They're not just holier than thou, they're holier than Christ on the cross. Why let facts get in the way of a good tantrum? They're not dreamy idealists, but vulgar, insulting, and tedious. See also Puritopian Emo Progressive