The Washington Supreme Court is on a roll. On March 11, it took the unprecedented step of outlawing mandatory sentences of life without parole for people under the age of 21—making Washington the first state in the nation to extend such protections to defendants who, while technically adults at the time of their crime, have greater potential for rehabilitation because of their youth. The previous month, a majority of the court struck down Washington’s drug possession law, effectively legalizing possession of controlled substances while overturning thousands of convictions going back decades. And, in January, the court made it easier for...