After four American and two British troops were killed in “insider attacks” in Afghanistan over the weekend, the U.S. military has halted joint missions between its troops and its Afghan trainees. Afghan government troops have turned on American soldiers repeatedly this year, killing a record 51. In the attack over the weekend, two Marines were killed, two jet fighters destroyed, and $200 million worth of damage was done to a heavily fortified base. American strategy and eventual withdrawal depends on training Afghan forces to take over security duties once the U.S. has left, but for now that is on hold. “We have got to do a better job at protecting our troops,” one official said.