Twitter appears in the book as both a vehicle for norm-breaking speech by the would-be autocrat most profiled in the book, Donald Trump, and as an example of one of the forces that has enabled Trump’s rise: the ascendance of new forms of media.

The authors include examples of tweets where Trump attacked media, political rivals like Hillary Clinton, and members of the judiciary. The broad audience Trump can reach on this platform amplifies the norm-breaking potential of this sort of speech, as a broad swath of the population is then inured to the idea that it is acceptable for an elected leader in the United States to demonize rivals, encourage violence, and question the validity of elections. The authors’ focus on Twitter shows how “mere words”—in this case, Trump’s tweets—act to undermine the stability of democracy.

While American democracy has faced the threat of would-be autocrats before, it has successfully resisted them, thanks in part to the invisible primary and party gatekeepers. But Trump surmounted these obstacles, thanks partly to the changing media landscape of the 21st century. Twitter is an important representation of these changes, and it’s part of the rise in social media that’s enabled figures like Trump to bypass gatekeepers in political parties and the media.