America’s network of libraries is vast, with 9,000 systems serving 155 million registered users. But that network is also under threat. While some communities are investing in modern new libraries, others are letting their branches crumble. Funding cutbacks for affordable housing or mental health services have led many low-income or unhoused people to use libraries as places of shelter. And widening polarization over social issues has sparked debates within some communities about whether some books should be banned as offensive. Despite the challenges, libraries play a civic role that many see as more vital than ever. “A democracy requires an educated public who are aware of the roles, responsibilities, [and] the powers that they have in just being citizens and taking part,” says Eric Klinenberg , a sociologist at New York University. “A library prepares you.…