Last month, the Supreme Court held in Monsanto v. Durnell that the Federal Insecticide, Fungicide and Rodenticide Act, in tandem with the Constitution’s Supremacy Clause, bars a state jury from punishing the maker of Roundup for omitting a cancer warning the EPA has repeatedly refused to require. The decision was right on the law. The reason has less to do with weedkiller than with who, in a country of 50 states and one federal regulator, gets to write the label. …Some other product will be next, in some other courtroom. The fight was never really about glyphosate. It was about whether one jury, moved by the suffering in front of it, can rewrite a judgment the rest of the country has to live by. The court’s answer means that a federally mandated warning has to mean the same thing in every state that reads it — and that whoever writes it has to account for everyone the jury never sees.