Craig was seen as a liberal voice on a variety Guantanaamo, torture, and release of the detainee photographs. Decisions on all these issues ultimately went against him. Time Magazine has recently written about his departure as has Maureen Dowd.
http://www.salon.com/news/opinion/glenn_greenwald/2009/11/24/civil_liberties/index.html-----
By embracing and defending numerous Bush/Cheney policies he once deplored, "Obama hasn't changed, just adjusted." He's learned secret things that he can't tell you about but which -- you should accept -- do justify his "adaptations." Whenever Bush followers would run out of arguments to defend their leader's actions, that's the same rationale they'd resort to: he knows secret things that you don't know and therefore we should trust him. So Obama has "learned" things that caused him to abandon his vehement condemnations of indefinite detention, state secrets, military commissions and denial of habeas corpus as unjust and un-American travesties and come to embrace them as important and necessary policies? Wow: that must have been quite an education. Don't he and his supporters owe George Bush and Dick Cheney a sincere apology for criticizing them all those years for these policies when, as it turns out, they were necessary and just all along? And see this insightful argument that makes a related point.
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So, to recap: we have indefinite detention, military commissions, Blackwater assassination squads, escalation in Afghanistan, extreme secrecy to shield executive lawbreaking from judicial review, renditions, and denials of habeas corpus. These are not policies Obama has failed yet to uproot; they are policies he has explicitly advocated and affirmatively embraced as his own.
There's more here, if you're interested
http://www.newamerica.net/publications/articles/2009/assassination_greg_craig_19901