His resiliency in the primary has caught the attention of the party establishment. Suddenly, Bernie Sanders’ presidential campaign is being taken seriously. For months the Vermont senator was written off by Democratic Party insiders as a candidate with a committed but ultimately narrow base who was too far left to win the primary. Elizabeth Warren had skyrocketed in the polls and seemed to be leaving him behind in the race to be progressive voters’ standard-bearer in 2020. Story Continued Below But in the past few weeks, something has changed. In private conversations and on social media, Democratic officials, political operatives...