Last September the Obama administration produced an FBI report that said mass shooting attacks and deaths were up sharply—by an average annual rate of about 16% between 2000 and 2013. Moreover, the problem was worsening. “The findings establish an increasing frequency of incidents,” said the authors. “During the first 7 years included in the study, an average of 6.4 incidents occurred annually. In the last 7 years of the study, that average increased to 16.4 incidents annually.”

The White House could not possibly have been...