Bergen : U.S. may be reluctant on U.S. due to role of al Qaeda -linked group . He says group has emerged as most effective rebel force and helps fill social needs . Peter Bergen : al Qaeda American affiliate attracts the most foreign fighters in conflict . He says group has shown ability to stage suicide bombings , threatens U.S interests .
Peter Bergen : U.S. may be reluctant on Syria due to role of al Qaeda-linked group . He says group has emerged as most effective rebel force and helps fill social needs . Bergen : Al Qaeda 's Syrian affiliate attracts the most foreign fighters in conflict . He says group has shown ability to stage suicide bombings , threatens U.S interests .