At 3 p.m. on Tuesday, August 18, the Swarthmore post office was empty. After a few minutes, clerk Nicole Scott emerged. Scott’s shift had been over for an hour, but she stayed on — without pay and against her postmaster’s advice — so the office wouldn’t have to close early. The Swarthmore facility had no one to cover the remaining hours, a problem the branch has been facing with increased frequency since overtime was eliminated over the summer. Lately, customers often find only one clerk behind the counter — if there’s anyone at all. What is happening in Swarthmore is happening in post offices across the country.