Despite concerns about the debilitating effects of partisanship on democratic government, in recent years political parties have gained strength in state governments as well as in Washington. In many cases these parties function as machines. Unlike machines of the past that manipulated votes, however, today's machines determine which candidates can credibly compete in a primary. Focusing on the history and politics of California, Seth E. Masket reveals how these machines evolved and how they stay in power by directing money, endorsements, and expertise to favored candidates, who often tend toward the ideological extreme. In a provocative conclusion, Masket argues that politicians are not inherently partisan. Instead, partisanship is thrust upon them by actors outside the government with the power to manipulate primary elections.