The Obama administration offered to work on Sochi Olympics security issues with Russia after a pair of bombings in Volgograd killed at least 31 people. President Vladimir Putin gave instructions to the National Anti-Terrorism Committee “to step up security measures across all of Russia and specifically in Volgograd region,” the Kremlin said Monday. “The president will receive daily reports from the NAC on the measures being taken along with regular situation reports.” Putin had not emerged to make a personal statement on the bombings, which occurred at a train station and on a bus. The train station bomber was reportedly...