I don't think there's such a thing as a born-again christian - once with God always with God.
We shouldn't judge peoples salvation based on their actions but on their hearts (which we are not capable of doing). I don't think we should be judging anyone on anything - especially their salvation and especially our leaders; as Paul remembers in Acts 23:5, a command from Exodus 22:28, "Do not speak evil about the ruler of your people." NIV
I think it's fine to question - but to judge in our hearts is to replace Jesus with ourselves - I dont think this is a good move!
As such, I dont think we can discern whether Bush is christian or not; least of all from media coverage.