A senior figure in the party whose departure from Chancellor Olaf Scholz’s coalition three weeks ago put Germany on the road to an early election has resigned in a furor over an internal document whose title referred to “D-Day.” Bijan Djir-Sarai of the pro-business Free Democrats said he was quitting as general secretary, the official responsible for day-to-day political strategy and election planning. The affair threatens to complicate further the Free Democrats’ campaign for an election in which polls already suggest they risk falling short of the 5% support needed to keep any seats in parliament.