— No one knows precisely where Abraham Lincoln delivered the Gettysburg Address. David Blankenhorn is explaining all this as he paces about the monument grounds dedicated to Lincoln’s famous speech at the Gettysburg National Cemetery. Fittingly, his outfit, touched by droplets of summer rain, could be described as contemporary Lincoln — dark suit, no top hat, with unassuming oxfords and a pair of rimless reading glasses dangling from a simple black T-shirt.