Sleeper cells

A member of the Syrian Democratic Forces (SDF) holds up the group’s flag at the iconic Al-Naim square in Raqqa, Syria, during the celebration of Raqqa’s liberation, Oct. 17, 2017. (Bulent Kilic, AFP/Getty Images).
A member of the Syrian Democratic Forces (SDF) holds up the group’s flag at the iconic Al-Naim square in Raqqa, Syria, during the celebration of Raqqa’s liberation, Oct. 17, 2017. (Bulent Kilic, AFP/Getty Images).