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gressive ambition. Indeed, he finds that party switchers pay a significant cost at the ballot box, one that is not foreshadowed in the elections immediately preceding the shift, and they also improve their committee assignments and influence when moving to the majority party. While Crossing the Aisle shows how employing rigorous social science methods allow us to better understand a phenomenon that occurs only rarely, it also has a richness that is rare in contemporary research on Congress and elections. Perhaps the most intriguing aspects of the book are the chapters based on interviews with legislators (both switchers and not) and party leaders. These interviews confirm many of the insights Yoshinaka develops in his theory and vividly illustrate the role party leaders play in inducing legislators to change parties. Majority party leaders have disproportionate electoral and institutional resources which they use to recruit members from the minority to join their ranks. Particularly remarkable is the description of a legislator who was in the process of deciding whether or not to switch parties. Consequently, the interviews provide insight into a legislator’s considerations and the order in which they address them as they contemplate making a switch. A legislator who began by considering the electoral consequences of the shift was enticed to complete it partly due to the increased power and influence he would hold once in the majority. Indeed, to the extent that the book has a weakness, it pertains to the application of the interviews and case studies. From a methodological perspective, some of the case studies and interviews might be more strategically selected to provide additional leverage necessary for addressing alternative hypotheses. Instead, in the case of the legislator who was in the process of making the shift, the results raise questions about the (small) role Yoshinaka ascribes to electoral considerations in the decisionmaking process. Even here, though, the finding does not mean Yoshinaka’s theory is wrong, as ex ante legislators may well believe they will get an electoral boost. This broader question would be a larger problem were the multi-method approach not employed, as unlike traditional case “only” studies, the evidence from them is not necessary for evaluating rival hypotheses. Consequently, such exiguous quibbles do little to detract from the force and findings of the work, as the evidence presented is at once clever and compelling. Overall, Crossing the Aisle is an interesting and impressive work. Yoshinaka’s multi-method approach synthesizing evidence from case studies, interviews, and massive amounts of historical legislative and elections data spanning decades illustrates how scholars can gain the leverage needed to provide insight into the causal processes that underlie rare events. Providing a rigorous yet accessible methodological account of party switching makes Crossing the Aisle likely to be of enduring interest to students and scholars alike.