Let’s assume that Hillary Clinton appoints at least one new net liberal to the Supreme Court during her term in office. In that scenario, the minimal composition would be five center left jurists, one idiosyncratic moderate conservative, one corporate conservative who has a fascination with “sovereign dignitude” and a pair of justices who think Lochner should be good law. The following scenario also works if any of the last four is replaced by another center left judge.
Let us assume that to get to that point it is fairly like that the Senate will go nuclear and abolish the filibuster as McCain indicated (and since walked back) that the Republicans consider a left of center Supreme Court majority to be fundamentally illegitimate even if it resulted from Democrats winning a lot of presidential elections in a generation or more.
Let us assume that at some point in the future there is a GOP trifecta. Let us also assume that a significant chunk of the future GOP’s base will be made up of people who strongly desire either an economically or culturally reactionary court.
With those assumptions, the following prediction is very easy to make.
When there is a GOP trifecta in Washington and a liberal leaning Supreme Court, the Supreme Court will see an increased number of justices equal to the difference between liberal and reactionary justices plus one.