From 2018 to 2020, the activist left experienced something of an electoral renaissance. It started, of course, when Alexandria Ocasio-Cortez, then an obscure primary challenger, ousted Rep. Joe Crowley (D-N.Y.), the chair of the House Democratic Caucus. The scope of the change was most evident, though, in how her win ― and the victories of the other left-wing candidates who would jointly come to be known as “The Squad” ― pushed many mainstream Democrats, including President Joe Biden, to the left.That ideological shift was, in turn, all the more remarkable because it was propelled by Justice Democrats, a small, millennial-run group that emerged from the ashes of Sen. Bernie Sanders’ first presidential run to recruit, consult and, if necessary, finance progressive primary challenges.Just o...