As he approaches the task of uniting the Republican party ahead of his all but official general election campaign, Mitt Romney will benefit from the same reality that's worked to his favor the entire race -- the composition of the Republican field. Specifically, Romney is fortunate that he had to beat out Rick Santorum to claim the nomination rather than Sarah Palin.
When Romney decided to seek the presidency for the second time, his moderate to liberal record in Massachusetts was bound to trigger a challenge from the right and set up a showdown, framed in shorthand, as the establishment of the party versus the conservative base. Had Palin been in the race as the conservative alternative, it would have been very difficult for Romney to attack her given the passionate following she has among many conservatives, because he wouldn't want to risk alienating them. Even if he had ultimately triumphed after a brutal primary fight, a lot of her loyal supporters would have found it difficult to bury the hatchet for the general election.
By contrast, Santorum came into the race with a very small following and was polling in the low single digits early on. Only when a number of other hopefuls fizzled did he emerge as the conservative alternative to Romney. Don't get me wrong, as I wrote earlier, I think Santorum raised his profile over the course of the race and proved to be a tenacious campaigner. But the point is that Santorum's support was as much about him being a vehicle for those who wanted to stop Romney than it was about a groundswell of support for him personally. His defeat is a disappointment to his supporters, no doubt, but less likely to sting as badly for as many people as a Palin defeat would have. Now that the primary is over, it will be a lot easier for Santorum voters to get behind Romney in the general election than it would have been for Palin given her built in fan base.