Iowa results - Surprising? Yes.  Shocking?  No

Conservative Republicans have tried to unify behind a single conservative candidate (Bachmann, Perry, Cain, Gingrich) without much success.  Santorum is the rising star.

Already this morning Michelle Bachmann has withdrawn from the race.  As the effective leader, Romney would presumably benefit from the withdrawal of candidates.  BUT NOT SO FAST! 

Keep in mind, as each conservative candidate withdraws, their supporters move on to  candidates of a similar political ilk.  For Romney, if Bachmann's withdrawal is followed too closely by Perry, and those supporters flock to Santorum, then Romney has trouble a brewing.  

He needs several more victories under his belt, before any more candidates withdraw.
At the same time, Bachmann & Perry's endorsement of Santorum (possibly conditioned on a future cabinet post) could generate the groundswell of support behind one conservative candidate.

Romney's best chance is a longer, prolonged primary battle, with all candidates staying on deck.  Upcoming debates also offer him the chance to bolster his conservative credentials.   However, given his current position, he probably feels he doesn't need to change a thing.
"Moderation" may Romney's operative word.   Of course, that was John McCain's campaign strategy, as well.  That's why today, former nominee McCain is endorsing Romney, as opposed to, you know, actually having won the Presidential election.