A judge declared a mistrial Thursday in the case of a former lobbyist caught up in the Jack Abramoff affair, the biggest setback in the government’s long-running prosecution of the influence-peddling scandal.

The jury deadlocked over allegations that Kevin Ring lavished thousands of dollars worth of tickets and meals on employees of then-Republican Reps. John Doolittle of California and Ernest Istook of Oklahoma and on Justice Department officials in return for congressional appropriations and other assistance for Abramoff’s clients.