As always, the modern American menu reads enticingly. Where else can a diner find short rib spring rolls, gumbo, a fried skate wing sandwich and Fuji apple-rhubarb tart under one roof? Unlike in years past, however, the execution here in Dupont Circle can be a mess. While generous with sausage and shrimp, that gumbo could double as a blast furnace, and the dessert comes to the table with a mere suggestion of rhubarb and dull pastry. Oysters on the half shell are still a good call, but the Asian-style duck sandwich is crazy-sweet with hoisin, the branzino sauteed to a stiff crisp and sitting on undercooked potatoes and bland fennel. Sadly, the espresso is as bitter as the family feud that saw the departure this year of everyone from the general manager to the chef to the talent behind what were once among the best desserts in town. “I recommend everything!” says the host of a gathering of suits in the clattery dining room, named for the lodging place in “Canterbury Tales.” I imagine he hasn’t eaten at the Tabard in recent months, when the service has slipped along with the cooking.