If one's criteria is sheer naked partisanship, it has to be Heller. It overturned decades worth of precedent in a remarkably strained reading of case law. And Heller's companion, McDonald v City of Chicago flies in the face of local government primacy and needlessly overturned a reasonable 7th circuit decision penned by noted liberal activist judge Frank Easterbrook. CU could at least point to Buckley's principle, even if it did overturn McConnell only a decade later.
Korematsu is handily the worst SC decision since the turn of the 20th century.
No,
Bush v. Gorefits the description of being a decision based on "sheer naked partisanship." Every Justice in the majority of that decision was a Republican, and the legal justification for why they felt they had to rule in Bush's favor was so lame that no one in the majority had the
cajones to take credit for writing the majority opinion. "Sheer naked partisanship," I take for granted, is distinct from ideological motivation. There is no other Supreme Court decision ever that was so blatantly motivated by sheer partisan loyalty .... five Republican Justices helped a fellow Republican clinch the election; the two Democrats on the Court at the time were among the dissenters.