Why does nobody seem to care that Isis has used chemical weapons?

A new era of chemical warfare is upon us—an era of chemical warfare as psychological warfare. The poisoning of Russian double-agent Sergei Skripal and his daughter in Salisbury, England, has dominated the headlines. But another development, from around the same time as the Salisbury attack first became known, is revealing for the attention it hasn’t received. Have you heard about the chemical weapons in Syria that don’t belong to Bashar Assad?