Both parties have their issues, but with things like this it’s always the Democrats, not the republicans.
And look at the actual court picks. The ones picked by R’s are the ones that side with the constitution. The ones from the D side rarely do. In a sane world, most supreme court decisions would be 9-0. This contant 5-4 thing is on the democrats.
Almost all justices slide leftward over time.
(also interesting that "median" Justice and Kennedy coincide of late; O'Conner was the median Justice before Kennedy. Roberts obviously will be picking up the mantle.)