But this doesn’t get it quite right, so we need to make some adjustments. First, the players themselves get to choose the referees. Second, they can collectively overrule the referees. Third, if enough of the players agree, they can rewrite the rules, even to the disadvantage of other players or the opposing team. Fourth, the players can make the crowd in the bleachers (U.S. citizens) play by the rules as well. Finally, the players can have a big influence on the people who aren’t even in the stadium (citizens of foreign countries).

While this is a more accurate picture, it’s also a more confusing one. But it does show something essential to the separation of law and politics: For a player, the rules can be either an obstacle to what she wants to achieve or a means of achieving it, depending partly on whether she can manage to change the rules.

People are willing to put up with such a system, even when it costs them a short-term gain, for three main reasons. First, they value the long-term stability that the rules achieve, because if those rules are applied consistently, outcomes of future conflicts are relatively predictable. Second, a consensus exists among the players that all sides will abide by the rules even when it costs a side one of these short-term gains. Third, the rules are supposedly impartial, not inherently favoring one side or another.

But for more than a century in American legal circles, this framework has been under attack. First came the legal realists, who denounced the very idea of an abstract, objective set of apolitical legal principles. Judicial decisions, the realists declared, were influenced just as much by what the judge had for breakfast—or what lurked in his Freudian unconscious—as by the impartial dictates of law. Next came the critical legal studies movement, a legacy of the New Left and the 1960s, best described as a strange bedfellows mash-up of Karl Marx and Harvard Law School. Judicial decisions weren’t unconscious at all, argued the crits: Judges had known all along that they were handing down diktats that favored the establishment while cloaking those decisions, and themselves, in the regal impartiality of the law, which in fact wasn’t impartial. The game, they contended, was rigged.

All of this by itself would have done a lot to blur the lines between law and politics, but it’s been helped along in the past half century by an inordinate amount of judicial activism. Activism is neither liberal nor conservative; rather, it can be used in the service of either philosophy. It’s simply what happens when a judge bases her decision more on her subjective beliefs about what the law ought to be than on an objective analysis of what the law currently is. Earl Warren is the textbook example. He had a classic response when hearing from lawyers who stated the law during oral argument before the Supreme Court. “Yes,” Warren would ask, “but is it right, is it fair?” Oliver Wendell Holmes’s statement from decades earlier was a prescient riposte to such activism: “I hate justice,” he wrote, “which means that I know if a man begins to talk about that, for one reason or another he is shirking thinking in legal terms.” Or, as he is supposed to have once told an idealistic advocate arguing for justice and fairness, “This is a court of law, young man, not a court of justice.”