Other GOP presidential candidates bubble up and down in the polls while Mitt Romney's support stays reasonably steady at around 25 percent (give or take) and usually first or second place, whence the notion that he's the inevitable nominee. But conservatives don't particularly like or trust Romney, and conservative candidates as a group outpoll him. If any of the conservative candidates could stop self-destructing for a few minutes, he or she would almost certainly beat Romney. But that appears to be a big if.
A coalition of conservative Republicans has launched an organization and website called Not Mitt Romney to catalog why they don't want him to win the nomination, attacking his ideology, politics, and even his electability (which is the one thing conservatives tend to like about him). While I don't share their political views, I think they make some good points about Romney, especially his almost comical inconsistency.
It's not unreasonable for people to changes their views over time. Most of us have done so. But Romney has completely reversed himself on gay rights, abortion, gun control, taxes, his own health insurance reform, and plenty more besides, in every case in a direction that would help him get the Republican nomination. I suspect the only thing he really believes in is that he'd like to be president. It's a mystery what Romney would actually do as president, except, I suppose, try to get reelected.