It might have been expected that a case involving the “dormant” commerce clause would split the justices of the Supreme Court in a less-familiar way than the one to which we’re accustomed, and yesterday’s decision on Maryland’s tax system did so: Justice Alito wrote the majority opinion, joined by Chief Justice Roberts and Justices Kennedy, Breyer, and Sotomayor. The others, including Justices Scalia and Thomas, who think the dormant commerce clause is an illegitimate judicial invention, dissented. Alito’s last two pages respond to the arguments of Scalia and Thomas, and do so, to my mind, persuasively. The idea in dispute is that the commerce clause, by giving regulatory authority over commerce among the states to Congress, cuts off that authority for states. It’s an inference from the Constitution that seems at least as well grounded as judicial review itself. For more on these issues, see here; for much, much more, see here.