How vulnerable are various Western Supreme Courts from devolving into the mockery that is the current US one?

In a non first past the post voting system, it's less likely that 1 radical party remains in power long enough to screw up the high courts. But it can still happen, case in point Hungary and Poland.

Iirc, Orban had been in power for many years in Hungary and went for a gradual erosion of the independence of the courts. Death by a thousand cuts.

Pis in Poland only had a majority for 2 election cycles, but they needed only the first win to screw up the courts. Instead of a gradual (legalistic) takeover, they went for a bonkers hostile takeover of the supreme courts: https://freedomhouse.org/report/analytical-brief/2018/hostile-takeover-how-law-and-justice-captured-polands-courts

The eu should have kicked out both states out of the decision making process and implemented sanctions, but since that required unanimity, Poland and Hungary were essentially protecting each other from consequences. Now that pis lost in Poland, I hope that the eu takes action and prevents this from happening again.