Steady political polarization since the late 1970s ranks among the most consequential transformations of American politics—one with far-reaching consequences for governance, congressional performance, the legitimacy of the Supreme Court, and citizen perceptions of the stakes of party conflict and elections. Our understanding of this polarization critically depends on measuring it. Its measurement in turn began with the invention of the NOMINATE algorithm and the widespread adoption of its estimates of the ideal points of members of Congress. Although the NOMINATE project has not been immune from technical and conceptual critique, its impact on how we think about contemporary politics and its discontents has been extraordinary and has helped to stimulate the creation of several similar scores. In order to deepen appreciation of this broadly important intellectual phenomenon, we offer an intuitively accessible treatment of the mathematics and conceptual assumptions of NOMINATE. We also stress that NOMINATE scores are a major resource for understanding other eras in American political development (APD) besides the current great polarization. To illustrate this point, we introduce readers to Voteview, which provides two-dimensional snapshots of congressional roll calls, among other data that it generates. We conclude by sketching how APD scholarship might contribute to the contemporary polarization discussion. Placing polarization and depolarization in historical perspective may powerfully illuminate whether, how, and why our current polarization might recede.

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Making a Rainbow Military Parliamentary Skill and the Repeal of "Don't Ask, Don't Tell" Rick Valelly When the Department of Defense was born in the late 1940s it arrived inside the cabinet with a significant prohibition: gay and lesbian citizens were not welcome to serve in America's armed forces 1 (Bérubé 1990, 261). The United States then went on to operate an officially "straight" military well into the 21st century. Congress contributed greatly to such longevity. In 1993, after initial opposition from President Bill Clinton, Congress enacted the "Don't Ask, Don't Tell" statute (DADT). It codified the proscription on gay and lesbian serviceand thus gave it new life. Congress indeed formalized the idea of a military closet. This 1993 statute recognized that many thousands of gays and lesbians bore arms but it held that their sexual orientation was inherently a threat to an effective military. Non-straight orientation was best kept secret. If a non-straight soldier were outed then the disclosure would lead to discharge. After 1993 only a statute enacted by both houses of Congress and signed by the president could truly recast the status of non-straight personnel in the U.S. military. The road to a "rainbow" military ran through Congress. That road would be difficult to traverse. Members of Congress would have to instruct the military that the criteria for service were flawed. But recent research has shown that members of Congress respond to pro-gay opinion in their districts only when it is exceptionally high and vocal (Krimmel et al. 2012). The number of House districts and states that fit these criteria is small. Not only would an unlikely congressional coalition for the repeal of DADT have to form, but repeal would also require a president willing and able to promote DADT repeal. Congress imposed DADT on an unwilling Commander-in-Chief, to be sure, but Congress would never dictate the reversethat is, the repeal of DADTto an unwilling president. Thus lifting the statutory ban on gay and lesbian military service also depended on the Democratic party hitting the Madisonian jackpotthat is, on unified control of the federal government. Of the two parties Democrats 75

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he sesquicentennial of the Civil War and the Reconstruction are upon us-and they will be for the next decade and more. Path-breaking scholarship about these epochs appears at a steady clip, inviting us to tear ourselves away from such current preoccupations as polarization, income inequality, and the struggle for social policy. "But wait," a busy political scientist would think, "isn't that better left to historians?" The scholar might reconsider that thought after absorbing the books under review, which communicate a great deal about public policy, political parties, leadership, and political transformation. They vividly remind us that destroying the world's largest system of slavery-which is what we did 150 years ago-was a world-historical accomplishment.Liberals and revolutionaries in Europe applauded the end of American slavery. Karl Marx was among those cheering for the Stars and Stripes. They knew something that we usually fail to recall-and can rediscover through the kinds of books under review. A stylized fact about nineteenth-century American politics is the relative inactivity and limits of national government. What our authors show, though, is how ambitious national public policy, partybuilding, and leadership were in the lead-up to the Civil War and during the Civil War itself. The daring aim of Reconstruction, to establish the world's first bi-racial democracy, had roots in a decade of "big"-in fact, really big-policy. The deeper lesson here is that the sesquicentennial period is our time as much as it is a time for historians.There's a striking leitmotif in these works-namely the role of transformative policy in bringing on the Civil War and in its conduct. Christopher Childers' study of "popular sovereignty" and Martin Quitt's biography of Stephen Douglas, the figure who thought most deeply about it, place us at one end of the historical arc: the Kansas-Nebraska Act. Kansas-Nebraska is a major case of a statute generating new politics, though hardly the politics that Douglas intended. It triggered the formal organization of the Republican Party and imposed sharp losses on Democrats in the 1854 elections. Equally important, it brought Abraham Lincoln back into national politics, but this time with a much higher profile.At the other end of the historical arc lies the Emancipation Proclamation. People often consider it symbolic-at most a statement of a change in the Union's war aims but not a substantive policy that actually emancipated anybody. There is nothing soaring about it. As Richard Hofstadter remarked, rhetorically the Proclamation has "all the moral grandeur of a bill of lading." 1 But as James Oakes shows, the Proclamation was the charter that ratified and expanded the policy process of making "freedom national." (Charles Sumner's 1852 Senate