I think going back on the promise he made in 2008 is more an indication about the entrenched power in the U.S. and the difficulty of making such a proclamation

I think going back on the promise he made in 2008 is more an indication about the entrenched power in the U.S. and the difficulty of making such a proclamation without knowing exactly what it would entail. For him to go back on this now would be a major blow to credibility. I doubt very much that he would announce this only to backtrack in a couple of months.