We can do a much better job of keeping criminals and terrorists out if we take screening processes seriously. In recent weeks the president and his senior homeland-security officials have pulled out all the stops to assure Americans that the vetting process for immigrants and foreign visitors is robust and thorough — but that even the most fabulous system, such as ours, cannot possibly be expected to prevent the entry of every person who means us harm, as demonstrated by the success of San Bernardino terrorist Sayed Rezwan Farook in obtaining a visa for his fiancée and fellow jihadi Tashfeen...