Shelby County v. Holder, decided Tuesday, struck down a key part of the Voting Rights Act (the part requiring certain states with a history of racial discrimination in voting to obtain federal permission in advance to change their voting procedures—called “preclearance”) as violating the “fundamental principle of equal sovereignty” of the states. This is a principle of constitutional law of which I had never heard—for the excellent reason that, as Eric points out and I will elaborate upon briefly, there is no such principle.

Section 3 of Article IV of the Constitution authorizes Congress to admit new states to the Union, as it has done many times, but says nothing about the terms on which they are to be admitted. Usually when new states are admitted it is on the same terms as the existing ones. But not always: Utah and several other western states were required as a condition of admission to outlaw polygamy—a novel condition. Not that any other state permitted polygamy. But other states, not having been subjected to such a condition when they were admitted, were free to permit polygamy without risk of being expelled from the Union.

It’s possible that the federal government would subject a state to unequal treatment so arbitrary and oppressive as to justify a ruling that Congress exceeded its constitutional authority. But Justice Ruth Bader Ginsburg’s very impressive opinion (in part because of its even tone), at a length (37 pages) that, remarkably, one would not like to see shortened—marshals convincing evidence that the reasons Congress has for treating some states differently for purposes of the Voting Rights Act are not arbitrary, though they are less needful than they were in 1965, when the law was first enacted.

Read more at Slate