Another day, another 2020 candidate announces a run for president. This time, it’s New York City Mayor Bill de Blasio who is throwing his hat in the ring, despite few pleas for the not-particularly-popular mayor to do so. So what sets de Blasio apart from the twenty-plus other candidates in the race? To de Blasio, it’s that he will run as a “national progressive icon.” That’s a bold strategy to differentiate himself, since Bernie Sanders, Elizabeth Warren and a host of others would probably too call themselves progressive icons. But if he’s going to run as an unabashed progressive, it’s worth delving…