Peter Bergen : Of al Qaeda 's affiliates , Al-Shabaab has had deepest links to the U.S . He says 15 Americans have died fighting for Al-Shabaab , including suicide bombers . Bergen : The U.S. government is trying to track down and kill a key figure in Al-Shabaab, Ahmed Abdi Godane. He says FBI , Justice Department have cracked down on American support .
Peter Bergen : Of al Qaeda 's affiliates , Al-Shabaab has had deepest links to the U.S . He says 15 Americans have died fighting for Al-Shabaab , including suicide bombers . Bergen : Ethiopian invasion of Somalia has played a role in stirring recruitment . He says FBI , Justice Department have cracked down on American support .