Nigeria’s governing party has started the process of choosing a candidate for next year’s presidential election. Under the constitution, President Muhammadu Buhari cannot run again, having served two terms. He has not publicly endorsed any of the 23 hopefuls who are standing at a meeting in Abuja of the All-Progressives Congress. Whoever wins will lead the party against the main opposition candidate, the former Vice-President Atiku Abubakar, in the election next February. The meeting has been overshadowed by the killing on Sunday of more than 20 Roman Catholic worshippers at a church in southwestern Nigeria.