Some presidential pardons are turkeys, sure. But a newly discovered one has echoed through the centuries to be particularly meaningful to the current president. On Sept. 1, 1864, an order from President Abraham Lincoln freed Moses Robinette from a military prison where he was incarcerated after being court-martialed over a fight in a Union Army camp during the Civil War. Robinette was President Biden’s great-great-grandfather. David J. Gerleman, a historian, documents the case in the Washington Post, using National Archives records. The tale is “an unknown piece of Biden family history,” Gerle…