With his country ensnared in mounting jihadist violence, bandit attacks and kidnappings, Nigerian President Muhammadu Buhari is under fire from allies and enemies alike for appearing incapable of tackling the security crisis. April saw an almost daily toll of bloody assaults and abductions in Africa’s most populous nation. In the past week alone, at least 240 people have been killed and more than four dozen kidnapped, according to tallies by local media. The fatalities included 19 Fulani herders gunned down in southeastern Anambra state; five students in the northwest who were shot to death days after gunmen snatched them from their campus; 31 troops, slain in a jihadist ambush in the Lake Chad region; and nine police killed by cattle thieves in northwestern Kebbi state. Senators, local go...