The Democrats seem to be convinced that Mitt Romney is going to be the GOP nominee. That is evidenced by the fact that David Axlerod and the DNC both have started targeting Mitt. If they are targeting him they must believe he's going to win.
That's a very plausible supposition on their part - Mitt Romney is a front runner in many states, he's well funded and he's well organized. He still fares best among GOP candidates in polls against President Obama. Further, his detractors have split their support among a few candidates. If the GOP primaries become a war of attrition, or simply longevity, he's got to be a favorite.
From the perspective of a non-Romney conservative, that might not be such a bad thing. It might be asking too much to thread this needle but here's my thinking. If the Democrats have their time and treasure focused on Romney for as long as possible, and he turns out to not be the nominee, that's all wasted time and money on the part of the Democrats.
There may be some additional benefit in that Democrat attacks on Romney would probably be helpful to the not-Romney candidates. The benefits of this sort of GOP misdirection are clear.
But it is a tough ask. What it means is keeping Romney in the top tier and competitive for as long as possible but ultimately ensure that he does not win. The chance of him winning remain strong if he remains competitive. And if after all that he wins, that Democrat effort at painting Romney in certain way - out of touch, say-anything flip-flopper are likely effective ground work for the general election.
Conversely, keeping someone else from running too far ahead of Romney may be difficult as well. If Romney doesn't run away with the state wins early it may become harder to keep him in the top tier rather than one of a large pack. A large pack may prompt the Democrats to keep their powder dry until they know at whom to direct their fire. If someone else becomes the obvious front-runner the Democrats would take their Romney efforts and re-point their efforts at whomever that is.
The best scenario is probably the least likely - the Democrats aiming at Romney and he goes away in favor of some other candidate. Even if it were possible, would anyone want to risk a strategy that keeps Romney in contention but ultimately has him lose? That's something his supporters and detractors can agree upon.