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on the hypotheses that the authors identify and test in the book. For example, the authors test whether repeal efforts are motivated by policy or by partisan brand considerations. In the end they see some support for policy considerations, but they conclude that “repeals are best understood as long-term contests between parties over the status quo in pursuit of electoral supremacy” (p. 146). Although their conclusion is reasonable, I do not think the results are as definitive as they claim because, as the authors note, disentangling policy preferences from partisan motivations is difficult at best (see their discussion on p. 104). The authors’ own analysis shows the difficulty in distinguishing partisan from policy motivations. They find that “homogeneous majorities that ascend to power after a long period out of power are more likely to succeed in their repeal efforts than are heterogenous and entrenched majorities” (p. 98). The authors conclude that this finding shows that repeals are driven by partisan motivations. However, this is not that clear because the finding has two dimensions. The first dimension is ideological: Is the majority party ideologically homogeneous or heterogeneous? This is plausibly related to policy preferences, and so it is not clear why this is evidence that partisan motivations are driving these repeal efforts. The second dimension is whether the party has recently become the majority party or has held that position for some time. This again could be related to policy considerations. The longer a party is in the minority, the more that existing policies are likely to be out of step with its preferences. Policy-driven politicians will want to bring these policies closer to their own preference, which could easily lead them to try to repeal bills that they did not like. Therefore, a party that recently ascends to power after a long period in the minority might do more to repeal bills not because of partisan considerations but purely because of policy considerations. To be clear, the authors may very well be right. I think there are good reasons to believe that partisan motivations—beyond policy considerations— motivate repeal efforts. I expect that future scholars will continue to build on the foundation created by Ragusa and Birkhead to more definitively answer that question. Future research will also use this data to test some of the arguments that the authors raise but do not test. Most prominently, they make a strong case that repeals are difficult, because once the law is passed it often creates a constituency that has interests in maintaining that law. If this is true, we would expect entrenched interests to help explain when and why repeals occur. Although the authors do not directly test this argument, some of their results suggest that interest groups are an important factor in repeal efforts. For example, they find that most successful repeals happen within 10 years of the law being passed (p. 47). This pattern is consistent with the possibility that the longer a policy is on the books, the more support it receives from groups in society, which then fight to maintain that law. One way to test this argument is to differentiate repeal efforts based on whether there are organized interests attached to them. Some laws, like the Affordable Care Act, might create groups with a vested interest in retaining the law, whereas other laws, like the National Maximum Speed Law, seem less likely to do so. Future research should more directly study the role of interest groups. Ragusa and Birkhead establish the theoretical importance of studying repeal efforts and provide the tools for quantitatively studying those efforts. These two contributions ensure that Congress in Reverse will be an important and impactful book for scholars seeking to understand the lawmaking process.