Pakistan, Feb. 8 -- Islamabad woke up bruised after the suicide bombing at the Khadija-tul-Kubra imambargah in Tarlai, but it did not stay still. Within a day, Interior Minister Mohsin Naqvi said four facilitators had been arrested in raids in Khyber Pakhtunkhwa, including what he called the "main mastermind" behind the attack. The message from the state was plain. The bomber may have been a body at the gate, but the chain behind him is being hunted.

That matters because the attack was not merely another entry in a grim ledger. It struck near the centre of power, under the gaze of its security architecture, during Friday prayers, in a city that sells itself as the federation's orderly face. Reuters and AP reported that Islamic State clai...