Leaders of Kenya's northeastern counties met this week and vowed to fight against al-Shabab, the Somalia-based militant group that has terrorized the region since 2011. One troubling question hung over the meeting: How can that be done effectively? The five counties represented at the two-day meeting ? Mandera, Garissa, Isiolo, Wajir and Marsabit ? all have seen their share of deadly al-Shabab attacks. The worst one took place in April 2015, when militant...