In a world of grandstanding and gavels, David Souter was a whisper — a Granite State recluse who slipped onto the Supreme Court in 1990 like a shadow through a side door, only to leave an indelible mark on American law and the politics of judicial selection. Appointed by President George H.W. Bush, Souter, who died this month at his home in New Hampshire at 85, was the “stealth nominee” who confounded conservatives, delighted liberals, and taught Republicans a lesson they’d never forget: Vet your justices, or risk a legacy that veers left.