For nearly half a century of American politics, conservatives have pulled off an astonishing trick. They have run successfully against the Supreme Court, railing against its rulings, its activism and its undemocratic character, and pledging to stock it with conservative justices. This has been a politically potent pledge, consolidating conservative support behind the Republican Party and its candidates for decades. The trick is this: The entire time, conservatives have been firmly in control of the court. After President Richard Nixon appointed four conservative justices, the liberal Warren court was gone from American life for good. Every year since then, conservatives have controlled at least five of the court’s nine seats.

Most Americans don’t know this. Nor are they aware of its profound consequences. Instead, most Americans hear and read a lot about liberal rulings the court has made in recent decades in a few high-profile areas, such as the constitutional rights of gay people. These are important, but they are exceptions; our attention to them obscures the rule. Adam Cohen’s new book, “Supreme Inequality: The Supreme Court’s Fifty-Year Battle for a More Unjust America,” attempts an enumeration of the broad consequences of the half-century-long conservative lock on the Supreme Court. Cohen takes us across a wide range of constitutional and statutory law, from school finance to criminal justice, all loosely tied to the theme of how the court’s turn to the right has led to more inequality. The book is a liberal cri de coeur, a lamentation of the many distinct and specific ways American society might be fairer, more equal and more humane if that one consequential change, the court’s decisive shift to the right under Nixon, had not occurred.

Nixon was lucky. He appointed four justices to President Jimmy Carter’s zero. But it wasn’t just luck. Much as Senate Majority Leader Mitch McConnell did half a century later when he blocked Merrick Garland’s nomination to the court, Nixon played constitutional hardball, hounding various liberal justices to resign. In the case of Abe Fortas, he succeeded, opening one of those four crucial vacancies that he would fill with conservatives. (Other opportunities came the usual way, as justices retired.)

Perhaps the most striking thing about Cohen’s book is the extent to which that moment, seemingly a historical footnote, becomes the fulcrum of the entire story, the key to understanding half a century of American constitutional politics and law. He returns to it throughout the book. For instance, in a discussion of Dandridge v. Williams, a consequential 1970 case in which the court ruled that it was constitutional for states to cap welfare benefits for large families, so there would be no additional money for families with more children, Cohen cites data showing that such caps lead to more children living in deep poverty. Then he adds, “As with the beneficiaries of the Warren Court’s rulings, the families who are further impoverished likely do not know the role the Supreme Court played in their lives — or that if Nixon had not driven Fortas off the Court, they might well be receiving uncapped welfare benefits.”

Most of the cases Cohen describes are well known to lawyers and law professors who work in those fields. But Cohen’s project is to bring these stories to a much broader audience. In that way, the book succeeds.

The book is less successful in drawing tight links between the court’s lurch to the right and the promise of the book’s title: an explanation of the rising inequality in the United States. The first chapters, which cover the rise and fall of the court’s rulings protecting the poor, are excellent. But explaining why the court pulled back from its project of protecting the rights of the poor does not really tell us why inequality has skyrocketed in this country over the past half-century. Cohen comes a bit closer in his discussion of how the court helped destroy unions and helped unleash the political power of the very rich through campaign finance deregulation. But the book is almost completely devoid of, for example, a discussion of antitrust law, where the shift toward keeping goods cheap for consumers instead of protecting competition may have done quite a lot to build the monopolistic, winner-take-all economy we now live in.

In many parts of the book, Cohen argues that the court has been too activist, in the sense of striking down duly enacted laws. In other parts, he says the court has not been activist enough — for instance, in protecting poor people or the victims of a racist criminal justice system. Cohen is not especially interested in interrogating the difference between these two lines of criticism. This is not that kind of book.

And fair enough: This is also not that kind of court. The Supreme Court that Americans have endured for the past 50 years has flipped the Warren court’s jurisprudence on its head, passively permitting extreme inequalities in school funding while rousing itself to strike down legislative actions aimed at promoting racial integration in schools. This is a court that somehow finds new rights in the penumbras and emanations of the Constitution to shield states from the Voting Rights Act and to protect large corporations from having to pay too much in punitive damages to people they have hurt. The dominant theme is not activism or passivity; not textualism or originalism; not pragmatism; not really any coherent jurisprudential philosophy worthy of an “ism.” The dominant theme is that the court’s high politics, its constitutional politics, has come to mirror that of the Republican Party, which has, over time and with enormous success, made appointing the right people to the court a centerpiece of its politics. Cohen’s book tells this story straightforwardly and well.

In that way, “Supreme Inequality” is “The Brethren” for our time. To be clear, I mean that Cohen’s book is utterly different from “The Brethren,” Bob Woodward and Scott Armstrong’s 1979 examination of the court’s inner workings — in a way that befits our current polarization. “The Brethren” covered the same period, the late 1960s and early 1970s, that is so pivotal in Cohen’s book, the period of the Warren court’s fall and the Nixon court’s rise. “The Brethren” used inside sources to tell a dramatic story of individual justices’ machinations and idiosyncrasies, full of surprises and accidents of history, rather than a story of the shifting tectonic plates of American constitutional politics. Cohen’s book is the opposite in every respect. Unconcerned with inside tales of intrigue and contingency, Cohen is content to simply tell us what the court decided. The book uses almost no inside sources. It offers precious few tales of internal drama. The drama, for Cohen, is there on the surface of the opinions. His story is much simpler than the story in “The Brethren.” But it is a story with one main virtue: It turns out, with the benefit of more years of hindsight, to be closer to the truth.

That story is basically this: From the Nixon era onward, our Supreme Court has become as polarized as the nation itself. Conservatives have held the crucial fifth vote. This story does not explain every decision of the court for the past 50 years. But it explains a very high share of the important ones, both the famous rulings and those a little further from the limelight, in which the court has worked gradually and with surprisingly little fanfare to unravel the achievements of the only significant period in American history in which it regularly sided with the poor and other marginalized people.

Supreme Inequality

The Supreme Court's Fifty-Year Battle for a More Unjust America

By Adam Cohen

Penguin Press. 416 pp. $30