For 230 years, the Supreme Court of the United States has been a political institution, but only rarely a partisan one. More than a century ago, the court controversially concluded that the Constitution required freedom of contract between employers and employees. The bare 5–4 majority that struck down a maximum-hours law for bakery workers in the infamous 1905 case of Lochner v. New York consisted of two justices nominated by Democrats and three nominated by Republicans. A Democrat dissented alongside three Republicans.


The era of Lochner was no aberration. The five-justice majority that consistently voted to strike down New Deal legislation three decades later included two justices who had been Democratic Party insiders, one of whom served as Woodrow Wilson’s first attorney general. The liberal Warren court of the 1950s and 1960s featured justices appointed by Republican President Dwight Eisenhower, including Chief Justice Earl Warren himself and the liberal icon William J. Brennan. Warren and Brennan voted with Democratic appointees like Arthur Goldberg, Abe Fortas, and Thurgood Marshall. Kennedy appointee Byron White often voted with more conservative Republican justices like John Marshall Harlan and Potter Stewart. So did Democratic appointee Justice Felix Frankfurter, who had been a member of Franklin Roosevelt’s Brains Trust in the New Deal.


In the nineteenth century, justices appointed by Whigs and by Democrats appeared on both sides of the momentous proslavery Dred Scott decision. Even the early–Reconstruction-era Supreme Court, which was dominated by justices appointed by Republican presidents during and after the Civil War, produced scrambled coalitions. The Slaughter-House Cases decision of 1873, adopting a narrow and crabbed reading of the Reconstruction Amendments, featured four Republican-appointed justices voting along with a justice appointed by Democratic President James Buchanan.
 

Today, by contrast, coalitions on the court are arranged almost exclusively along party lines. In a 2016 study, legal scholar Neal Devins and political scientist Lawrence Baum showed a sharp increase in important decisions characterized by a strictly partisan split after the confirmation of Democratic appointee Elena Kagan to what had been Republican appointee Justice John Paul Stevens’s seat. We are now at least one decade into a nearly unprecedented experiment in partisan judging at the highest court in the land. Our legal and political systems have barely begun to process what that means.