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.