WASHINGTON — When the Supreme Court issued its latest campaign finance decision last month, the justices lined up in a familiar way. The five appointed by Republican presidents voted for the Republican National Committee, which was a plaintiff. The four appointed by Democrats dissented.

That 5-to-4 split along partisan lines was by contemporary standards unremarkable. But by historical standards it was extraordinary. For the first time, the Supreme Court is closely divided along party lines.

The partisan polarization on the court reflects similarly deep divisions in Congress, the electorate and the elite circles in which the justices move.

The deep and often angry divisions among the justices are but a distilled version of the way American intellectuals — at think tanks and universities, in opinion journals and among the theorists and practitioners of law and politics — have separated into two groups with vanishingly little overlap or interaction. It is a recipe for dysfunction.