A field office for Michael R. Bloomberg’s presidential campaign in Knoxville, Tenn., was vandalized overnight, the latest in a series of vandalism incidents that prompted top campaign officials to blame Senator Bernie Sanders for the attacks.

Campaign volunteers arrived at the office on Friday morning to find profanity spray-painted across the glass front doors. Handmade posters, reading “Authoritarian,” “Classist” and “Oligarch,” were plastered on the windows. Mr. Bloomberg, the former mayor of New York City, is a multibillionaire who has spent hundreds of millions of dollars of own money on his campaign so far.