The ever-widening investigation of the San Bernardino terrorist massacre has revealed at least two dubious marriages that experts say expose huge loopholes in the immigration system and continue to put national security at risk. Federal authorities have charged Enrique Marquez with marriage fraud for his allegedly sham union with Mariya Chernykh, a Russian woman whose sister married the brother of terrorist Syed Rizwan Farook after first gaining residence through an earlier marriage. And of course, Farook's own wife, Tashfeen Malik, who was killed along with him in a shootout with police following their Dec. 2 attack, married her way into...