I mostly agree with this Jonathan Chait post — obviously there are major differences between Republican-appointed and Democratic-appointed judges, and those differences have grown over time — but he’s wrong about this:
Several decades ago, there really was a vast gulf between the workings of the Court and the political agenda of the politicians who appointed its members. The ideological character of Supreme Court justices had only a loose relationship to the ideology of presidents who selected them. Byron White, a Kennedy appointee, frequently joined conservatives, while some of the Court’s most liberal members, like Harry Blackmun and David Souter, were Republican appointees.
But this is no longer true, for one main reason: Republicans decided this level of unpredictability was incompatible with their goal of reshaping the courts along conservative lines.
Byron White is Chait’s best possible example of a Democratic appointee who sided with conservatives. He was appointed in 1962. His Republican examples joined the Court in 1970 and 1990, and additional examples from the 1980s could have been mentioned.
Democratic presidents and candidates, beginning with Bill Clinton, said they were looking for judicial appointees they could trust to support unrestricted abortion. Republican presidents rarely made the opposite stance an explicit litmus test, with George W. Bush successfully resisting pro-life efforts to create one during the 2000 campaign. In the 1980s and 1990s, Republican senators were more likely than Democrats to insist that it would be wrong for them to apply any ideological test to nominees, and therefore they voted for Democratic nominees more than Democratic senators voted for Republican ones.
The political polarization of the courts was probably inevitable once their role in making public policy expanded. For a variety of reasons, though, it was the Democrats’ appointees who became politically reliable partners in their coalition first, and Democratic political activists who insisted on it first. Republicans were late to adjust to the new dispensation.