I have written this longread for TPM, and I’ve been working on it for quite some time.  It begins:

When the next President of the United States assumes office on January 20, 2017, Justice Ruth Bader Ginsburg will be nearly 84, Justices Antonin Scalia and Anthony Kennedy will be over 80, and Justice Stephen Breyer will be 78. Although many Justices have served on the Court into their 80s and beyond, the chances for all of these Justices remaining through the next 4 or 8 years of the 45th President are slim. Indeed, the next president will likely make multiple appointments to the Court.

The stakes are high. On non-controversial cases, or cases where the ideological stakes are low, the Justices often agree and are sometimes unanimous. In such cases, the Justices act much like lower court judges do, applying precedents, text, history, and a range of interpretative tools to decide cases. In the most controversial cases, however—those involving issues such as gun rights, affirmative action, abortion, money in politics, privacy, and federal power—the value judgments and ideology of the Supreme Court Justices, and increasingly the party affiliation of the president appointing them, are good predictors of each Justice’s vote.

A conservative like Justice Scalia tends to vote to uphold abortion restrictions, strike down gun restrictions, and view the First Amendment as protecting the right to spend unlimited sums in elections. A liberal like Justice Ginsburg tends to vote the opposite way: to strike down abortion restrictions, uphold gun laws, and view the government’s interest in stopping undue influence of money in elections as justifying some limits on money in politics. This to not to say it is just politics in these cases, or that these Justices are making crassly partisan decisions. They’re not. It is that increasingly a Justice’s ideology and jurisprudence line up with one political party’s positions or another because Justices are chosen for that very reason.