A novel explanation for why politicians insult, accuse, and threaten their opponents, even though voters say they don't like it. Why do politicians engage in nasty politics? Why do they use insult, accusations, intimidation, and in rare cases violence against their domestic political opponents? In Nasty Politics, Thomas Zeitzoff answers these questions by examining this global political trend in the US, Ukraine, and Israel and looking at how key leaders such as Trump, Zelensky, and Netanyahu use it. Drawing on surveys, case studies, in-depth interviews, databases of nasty politics, and large social media datasets, Zeitzoff shows that across all three countries, the public generally doesn't like nasty politics and it increases the threat of political violence. But it can also be a way to signal toughness to voters, which is especially important in threatening times. Featuring a powerful theory of why nastiness takes hold in democratic polities, Nasty Politics highlights how it influences the kinds of politicians who run for office and deepens our understanding for why so many politicians now rely on outsized anger and withering insults for political gain.