As Washington State Department of Licensing v. Cougar Den illustrates, not all 5-4 Supreme Court cases involve high-profile, controversial issues where the Justices are divided on ideological lines.
In this case the Supreme Court held 5-4 that a treaty forbids the State of Washington from imposing a tax upon members of the Yakama Nation that import fuel.
An 1855 treaty between the United States and the Yakama Nation reserves to the Yamakas “the right, in common with the citizens of the United States, to travel upon all public highways.” A Washington statute taxes fuel importers who bring large quantities of fuel into the state by ground transportation. Cougar Den is a wholesale fuel importer owned by a Yakama member that transports fuel by truck from Oregon to Yakama-owned gas stations in Washington. Cougar Den argued the treaty preempted the tax.