The president of Brazil's governing PT has resigned and four of its members have been expelled over their roles in a botched smear campaign against members of the opposition in the run-up to presidential, congressional and state elections.

Ricardo Berzoini, the former party president, has come under severe pressure to go since President Luiz Inácio Lula da Silva was forced into a second-round run-off. The botched smear campaign was seen as a main cause of what amounted to a shock defeat.

Mr Berzoini, who stood down as leader of Mr Lula da Silva's re-election campaign after the first round, had resisted calls for his resignation from the party leadership, arguing that the job was an elected post. He appeared to have Mr Lula da Silva's support: the president said on Friday there was "no need to take any political decisions now, while the process is still unfolding". But Mr Berzoini eventually announced his resignation on Friday evening after a meeting of the PT's national executive, which also expelled four party members accused of direct involvement in the affair. A fifth member faces disciplinary proceedings.

By taking such firm action, the party may be trying to help the president's re-election campaign by showing itself to be quick in dealing with wrongdoers and by helping to put the scandal in the past.

Yet the opposition will do everything it can to keep the issue alive. They will be helped by a police investigation into the affair. Federal police said they would call Mr Berzoini for questioning next week.

Police are looking into the origins of R$1.7m ($788,000) found in the possession of PT members who were preparing to buy information purporting to implicate in a corruption racket the PSDB's candidate for governor of São Paulo state.