Let’s indulge in a bit of political fantasy. It’s January 20, 2021. After a long and grueling campaign, Bernie Sanders, a rumpled, cranky democratic socialist who spent his entire political career on the margins of mainstream political life, is sworn in as president and assumes the most powerful political office in the world. What kind of political terrain does he inherit?

Let’s start with a basic constraint socialists face in any capitalist country: private control over investment decisions, which governments depend upon for steady economic growth, tax revenues, and legitimacy. A Sanders victory probably would have tanked the stock market and generated a crisis of “business confidence,” laying siege to his administration before Bernie could even take the oath of office.

In addition to these built-in capitalist constraints, Sanders’s agenda would have run headlong into America’s political institutions, which, for democratic socialists and everyone interested in a more just society, amount to one giant collective action problem.