The much-awaited testimony of Rick Gates—a star witness in the tax and bank fraud case against Paul Manafort—ended in courtroom fireworks Monday as the judge overseeing the case tangled with a U.S. prosecutor over how to speed up his questioning.

On the fifth day of the former Trump campaign chairman’s trial in Alexandria, Virginia, the government’s crucial witness—and the man Manafort’s attorneys will attempt to discredit—testified to committing bank and tax fraud with his former boss. Gates, who will continue testimony Tuesday, told jurors he was often working under Manafort’s direction.