What is ISIS-K, Terror Group Believed to Be Behind Kabul Airport Attack?

Officials have not confirmed it, but terror group ISIS-K is believed to be behind the explosion that killed more than a dozen U.S. servicemembers and 60 Afghans at the Hamid Karzai International Airport in Kabul, Afghanistan Thursday. Former CIA analyst and U.S. Army member Matt Zeller explains what he knows about the group.