He also said, for the first time, that he believed he should have pressed immigration reform — he had come to office calling it his first priority — instead of calling for an overhaul of Social Security after the 2004 election.
This strikes me as a much bigger concession than it might appear. Which is to say, doing immigration instead of Social Security in 2005 wouldn't just have been tactically smarter. It would have signalled a completely different approach to his second term, in which he spent his famous "capital" doing something potentially unifying rather than something incredibly divisive and overwhelmingly unpopular outside his wealthy supporters.
Update: Alex Massie has some smart thoughts on this, too.