Sure, it is implausible that a self-described “socialist” with a gruff Brooklyn demeanor could actually win. But as the Washington Post reported last month, “Even Clinton’s skeptics acknowledge the difficulty of derailing her juggernaut,” so their hope is that a primary challenge can “shape the debate and pull Clinton to the left on issues.”

Sanders, who has stressed that he would “not [be] running to attack Hillary Clinton,” is perfectly suited to play that role. A Clinton-Sanders primary – assuming Sanders could generate enough support to force Clinton to engage – would be serious debate over the issues progressives care about, not a personality clash with scorched-earth attacks that could weaken the eventual nominee for the general election.

Apparently, the reason for the lack of interest lies in progressives’ collective hunger for The Next Big Thing. For the economic populists, Warren’s mix of Okie folksy charm and Harvard intellect is a fresh face that can expand their gospel beyond the already converted. Sanders may have a case to make that he has real experience building ideologically diverse coalitions around populist issues. But today’s Vermont is so deep blue, people have forgotten than Vermont was much more Republican when he first won statewide in 1990.