I've been saying this for weeks. His tone has changed significantly since he started getting the briefs.
I have long suspected that there is some Terrible Knowledge that is revealed to the president-elect just before he assumes the office. Obama’s demeanor started to change right around the same time as he went in for his first briefing. Once the Insiders (for lack of a better term) revealed the Big Secret (for lack of a better term) to him, Obma suddenly realized the magnitude of the task ahead, and all that hope ‘n’ change stuff suddenly seemed rather unimportant and stupid.
Perhaps we have reason to hope that Obama might be a decent president after all.