I'm not really sure why the New York Times would poll this question, but it's a deeply stupid one. Unless one can read minds, the personal motivations of individual politicians are unknowable.
This is why I was never much interested in why George W. Bush wanted to invade Iraq. Was it PNAC, revenge for Daddy, the oil -- or blowing shit up for Jesus? Who cares? And how can you know?
All that matters to me is getting the policy right. Everything else is a waste of time.