Primaries may contribute to polarization in other ways than a selective effect emanating from voters. This chapter tests a second potential mechanism of polarization, where incumbent members of Congress may respond to being challenged in a primary by adopting more liberal or conservative voting patterns in subsequent congresses. To test incumbents’ responses, it uses a series of fixed-effects models, clustered at the representative level, with roll-call movement as the key dependent variable. When considering the universe of all primary challenges, incumbents do not respond positionally, but when primaries are ideological and factional, they move toward their ideological pole. These effects are larger for factional primaries, indicating that incumbents are most responsive when a primary opponent has the support of an alternative party faction. These effects are larger for Republican than Democratic members of Congress, which is one way in which primaries may contribute to asymmetric polarization. These findings indicate that primaries may matter for polarization because incumbents believe them to be important and so are responsive to them.

The November 2020 elections delivered a big victory for Democratic presidential challenger Joseph R. Biden along with gains or holds for many Republicans running in congressional and state contests. Reinforced partisan divisions were not, however, the most remarkable aspect of this election. Amid a raging deadly pandemic and sharp economic retraction, about two-thirds of eligible Americans registered their votes by mail or in-person, marking the highest eligible voter turnout in more than a hundred years. Some 74 million voted for Donald Trump, while more than 81 million supported the winner, Joe Biden. This remarkably high voter turnout continued through the early January 2021 Georgia runoffs, where upset victories for Democrats Jon Ossoff and Raphael Warnock delivered control of the US Senate to their party through 2022. A modern US electoral system that has, for decades, exhibited extraordinary slack in voter participation suddenly experienced engaged citizens on both ends of the partisan spectrum, as many more Americans than the usual ideologically attuned elites, interest groups, and party-oriented activists, jumped into a high-stakes, emotionally and morally infused referendum on the meaning and future of US democracy.

Starr describes how we have became so vulnerable to disinformation in this digital era. Heargues, that, like analyses of democratization, which have turned in recent years to thereverse processes of democratic backsliding and breakdown, analyses of contemporarycommunication need to attend to the related processes of backsliding and breakdown inthe media – or what he refers to as “media degradation.” After defining that term inrelation to democratic theory, Starr focuses on three developments that have contributedto the increased vulnerability to disinformation: 1) the attrition of journalistic capacities; 2)the degradation of standards in both the viral and broadcast streams of the new mediaecology; and 3) the rising power of digital platforms with incentives to prioritize growthand profits and no legal accountability for user-generated content. Neoliberal policies oflimited government and reduced regulation of business and partisan politics contributed tothese developments, but while demands are growing for regulation, it remains uncertainwhether government can act effectively.