Her sharpest words were not in the body of her opinion. They were tucked away in a footnote. That subtle placement speaks volumes about Ketanji Brown Jackson, the supreme court’s newest member and already its fiercest liberal voice. The footnote in question can be found in Trump v Casa, the June ruling that gave a big boost to Donald Trump by clipping the wings of federal judges and limiting their use of nationwide injunctions to block the president’s worst excesses. Over 21 pages of taut dissent against Casa, Jackson decried the 6-3 ruling as “an existential threat to the rule...