Senator Bernie Sanders won 13 million votes and a majority of young voters in the 2016 Democratic primary, giving a consensus unbeatable party favorite, Hillary Clinton, a shockingly close challenge. He emerged from the presidential election as the most popular politician in the US, despite being a 75-year-old self-professed “democratic socialist.” What lessons can be drawn from this surprising but—in the end—losing campaign, and what to make of the direction the Sanders movement has gone since the election? Vermont native Heather Gautney is a senior policy advisor to Bernie Sanders in his Washington, DC office and was a senior researcher on his presidential campaign. The author and editor of several books on social movements and American politics, she brings her scholarly expertise and left politics to bear on the scenes and conflicts she witnessed from inside the campaign and inside the Beltway. This is both an insider's sympathetic view of the Sanders phenomenon and a skeptical left scholar's view of its limitations. In reviewing what enabled Sanders to reach out to an unprecedented number of people with a socialist message, she draws lessons about the prospects and perils of building a leftist movement in the United States. Gautney’s reflections on the role that race and class played in this election cycle and analysis of the prospects and perils of the Democratic Party will advance the passionate debate over how to build a progressive opposition to Trump and a lasting left movement in America.