Ever since Gibbons v. Ogden (1824), the basic idea has been that the Constitution’s Commerce Clause forbids, of its own force and without any congressional act, state laws that discriminate against interstate commerce; impose grossly disproportionate burdens on such commerce; or, as here, regulate on a wholly extraterritorial basis. Until 1983 or so, when latter-day originalist justices discerned that this “dormant” Commerce Clause is a wholly illegitimate judicial invention—the kind of constitutional common law forbidden by (you guessed it) Erie Railroad.

The answer to that derangement is supplied in a splendid amicus brief on behalf of the Chamber of Commerce by Professor Michael McConnell (Stanford) and Steffen Johnson (Wilson Sonsini).