To almost no one's surprise, days before Roger Stone's prison sentence was about to begin, President Donald Trump has spared his long-time political crony from the pen — late Friday, Mr. Trump commuted Stone's sentence. It is time for New York prosecutors to answer this latest assault by Trump on the rule of law: They should ready a state prosecution of Stone. Bringing a new case against Stone is possible thanks to Governor Andrew Cuomo and the New York Legislature for Assembly Bill 6653. Signed into law last October, AB6653 enables New York district attorneys to prosecute what effectively amounts...