To President Franklin Roosevelt’s dismay, a Supreme Court bloc of six conservative justices struck down key parts of the New Deal in the 1930s. But by 1945, there was an FDR bloc. He had appointed all nine justices. For much of the 1960s, a liberal bloc was in command. It’s hardly a surprise when a group of Supreme Court justices makes a point of voting alike. But today’s liberal bloc is different than those of the past. The four liberal justices are not in charge, yet they play a more prominent role than most minorities. This is no accident. They plot to speak with one voice and usually succeed. They’re motivated, cohesive, and disciplined. As a result, they punch above their weight. The liberalism of all four is reliable, though not identical. Judging by their...