I've seen some critics of the GOP say the party in power makes no difference to Supreme Court rulings. But that's a gross oversimplification.
For instance, they point out that Justice Kennedy was nominated by a Republican president. But that overlooks two salient facts:
i) Reagan originally nominated Bork. That was his first pick.
ii) At the time, Democrats controlled the Senate.
If Democrats control the Senate, then a Republican president, no matter how conservative, can't push through a nominee that Democrats oppose.
There's also the mathematical fallacy–as if it came down to one vote: Kennedy's. But the four justices who opposed homosexual marriage were Republican nominees, while four of the five justices who supported homosexual marriage were Democrat nominees. It took five votes, four of which were supplied by Democrat nominees.
Therefore, it's counterproductive to use that as an example of how the party in power makes no difference to how cases are decided. The reality is precisely the opposite.
The four Democrat nominees were nominated by Bill Clinton and Obama respectively. If their Republican rivals had won instead, that would be four additional Republican nominees. Even if two of them turned out to be closet liberals, you'd still have a working conservative majority.
Likewise, I've seen some critics single out Chief Justice Roberts, who was nominated by a Republican, because he voted for Obamacare. Yes, Roberts disgraced himself on that issue. But what makes that the litmus test? Roberts voted against homosexual marriage. Why not make that the litmus test? Imagine how much worse the court would have been had Kerry or Gore been president.
Also, what about good nominees like Rehnquist, Thomas, Scalia, et.? Why don't Republican presidents get credit for them? And it's not as if presidents have a crystal ball.