Noah Schachtman at Danger Room says:
Carter served as deputy assistant secretary of defense for detainee policy, handling porcupine-thorny issues like Guantanamo. So when Carter said he was stepping down for “personal and family reasons,” some wondered whether that was Beltway code for unhappiness with the way the Obama administration was dealing with Gitmo. After all, every D.C. official says he or she’s resigning to get in more family time.
I just got off the phone with Carter. “I know this is a Washington cliche, but sometimes the cliches are true,” he tells me. “I made this tough decision for personal reasons, even though I loved the job and the work we were doing. Hopefully I’ll have the chance to serve again.”
Schachtman claims to be a long-time friend of Carter's and believes him. Carter has always seemed like a stand-up guy to me, so I tend to believe this.