Will Nukes America: National Command Authority

This short story begins with the POV of a rural Maryland judge (Eastern Shore), sitting in his home after the nukes hit. To the west he can see the DC nuke, to the north a mushroom cloud rises above Dover. He hears a chopper and thinks nothing of it. Maybe 20 minutes later there's an urgent knock on the door. It's the sheriff and a couple of men in suits. The sheriff explains that these are secret service agents and they need someone to swear in the president.