The Ft. Hood Massacre in November 2009. The American Consulate in Benghazi in September 2012. The Boston Marathon Bombing in April 2013. San Bernardino in December 2015. All were acts of terror on American soil, but San Bernardino is different. Very different. In July 2009, Major Nidal Hasan, a devout Muslim, bought a high capacity, automatic weapon, and practiced shooting it. In November, ostensibly unhinged about a deployment to Afghanistan, Hasan walked into the Soldier Readiness Center—where for several years personnel had experienced his Islamic rantings—and after a shout of Allahu Akbar—systematically murdered every person in uniform he saw. Thirteen...