Switching parties is arguably the most important decision a politician will ever make. This book is the first-ever systematic study of the causes and consequences of legislative party switching in the United States. The author argues that re-election alone does not explain party switching. He proposes an ambition-based theory that accounts for multiple goals (including higher office aspirations and the desire for influence in the legislature) with a focus on the electoral costs and the institutional benefits of the decision. The book combines the statistical analysis of electoral data and legislative careers in the US Congress and state legislatures with elite interviews of party switchers, non-switchers, and a party leader. The case study of a party switcher's decision in 'real time' documents the complexity of the decision in a politician's own words prior to and following the switch. The book raises important questions regarding the meaning of a party label.

'By focusing on ambition - both the desire for higher office and the goal of influencing policy deliberations, Crossing the Aisle offers a compelling analysis of party switching in the US Congress and state legislatures. Yoshinaka combines keen theoretic insights with thoughtful empirical work to produce a quantum advance on previous work, with deep consequences for our understanding of election outcomes and policy-making.'

William Bianco - Indiana University, Bloomington

'Crossing the Aisle is the definitive book on party switching in legislatures. It is novel, provocative, and upends much of the scholarly conventional wisdom about how parties constrain the choices legislators make. An important implication of Yoshinaka's book is that elite party affiliation is much more fluid and negotiable than scholars theorize and pundits assume. This book raises important, and at times counterintuitive, implications about how well political parties can control their own legislators. It is one of the best books on political parties I have read in some time, and it is a must read for those interested in understanding legislative politics, elections, and representation.'

Christian Robert Grose - University of Southern California

'This is the first in-depth, book-length treatment of party switching. Although a rare phenomenon in the US, party switching has important consequences both for individual careers as well as for legislative parties overall. Drawing upon both elite interviews and data analysis, Yoshinaka persuasively contends that career ambition - both for intra-institutional leadership positions, as well as for higher office - is a critical factor driving the often risky and costly decision to change parties.'

Frances Lee - University of Maryland, College Park

'I am amazed by the conceptual and theoretical range that Yoshinaka has been able to develop from studying what is empirically a relatively rare event. The links he establishes between his analysis of party switching and the legislative elections literature, the committee assignment literature, the work on ambition theory, and material on rare events means that the research findings have broader implications that go beyond a narrow focus on party switchers. In sum, I find that in both substantive and methodological terms, Yoshinaka’s book is first rate.'

Bruce Oppenheimer - Vanderbilt University, Tennessee

'Yoshinaka claims, correctly, that this is the first systematic, book-length study of party switching by legislators in the US … Recommended. Upper-division undergraduates through faculty.'

J. C. Berg Source: Choice

'By analyzing members’ decisions to switch parties (or not) in the postwar era, Antoine Yoshinaka provides important and at times unexpected insight into all members’ partisan identities, and into legislative party organizations more generally. Crossing the Aisle is a must-read for those interested in the U.S. Congress, legislative behavior, political parties, and partisan identification.'

Kathryn Pearson Source: Congress and the Presidency