I have long thought that the reason for Romney's flip-flopping is not because he is a supremely ambitious person without core beliefs, but rather because he is a supremely ambitious person who has been hiding his core beliefs from the public. And I think you can find his core beliefs in the teachings, mores, and policies of the Mormon church.
Given that Romney is such a high-profile pillar of that church, holding a number of important posts, you would expect that his true beliefs would match whatever the church says they should be. He would not be able to hold such positions in the church otherwise.
If Romney had run for senator and governor in Utah or some other more conservative state, he would never have had to take all those liberal-sounding positions that he claimed in Massachusetts. He could have sincerely and consistently expressed his Mormon-inspired world view and still have been a viable candidate.
But his base was Boston. He probably genuinely likes Massachusetts and saw things in the state that, if he ran things, would be better (in his mind). Since a lot of the core Mormon ideas (including being aggressively secretive) go over like lead balloons in a state like Massachusetts, he had to hide them from the state’s voters. Thus his claims to being more liberal than Ted Kennedy or his comments that he was not a lockstep follower of the Republican party line. And that was reasonable political calculus back in the good old days of 1994-2002.
Then the Tea Party threw the old calculus out the window. Now he had to be “severely conservative” (as well as backed by hundreds of millions of dollars) in order to get ahead in the Republican Party. Luckily for Romney, he was “severely conservative” in his heart and mind because the causes that get the Tea Party fired up are so similar to what he absorbed as a young Mormon, what the Mormon church has perpetuated in its policies, and what Romney apparently still believed (if the behind-the-scenes reports of his actions as governor are true). The rest of that stuff in Massachusetts—health care, equal rights, weapons bans, etc., were aberrations—things he needed to say and do to get elected. And since he didn’t believe in that stuff, he could easily (in his mind) change his story about those things.
Romney’s penchant for lying about his past statements and actions--and his apparent disregard for Youtube-type evidence--notwithstanding, it is abundantly clear how he will operate if elected President. He will be a radical conservative in social policy, unabashedly pro-business in economic policy, and a rabid neo-con in foreign policy. That’s what is at his core, that’s what he was hiding when running for office in Massachusetts, and that’s what he has figured is okay to let out now that the Tea Party is riding high.