Sounds like his conscience finally got to him. He knew all along that opposing embryonic stem cell research could not be justified on any objective scientific grounds. But he's working in politics now, and did what he thought he had to do, and lied. Now he has stopped lying. I respect him for it.
Good grief.
There's precious little that 'objective scientific grounds' can be used to oppose; there was a lot of really nasty behavior supported on 'objective scientific grounds' in the last century and Peter Singer is doing his best to continue that work in this century.
This is a moral and ethical issue, and Frist caved.
With any luck, he will be shown to be mistaken on the political impact as well.