If Mitt Romney loses this November--as I believe is more likely than not--there's going to be a lot of post-mortems on how this happened and whether there was anything he could have done differently. Conservatives are going to argue that Romney wasn't sufficiently conservative enough and didn't "stand for something" or "attack Obama hard enough" (this comes from laughable characters like Donald Trump and Sarah Palin) but I think they have this wrong. Romney has been saying everything he could to ally himself with his party's right wing, and his reflexive criticism of Obama has gotten predictable, to the extent that if Obama stopped for a burger on the way home Romney would point out that the burger stop took precedence over attending a funeral for war veterans.
The real failure as I see it was that Romney did not take advantage of opportunities to recapture the political middle. As a moderate Republican (at least until 2007) whose background is more Michigan and Massachusetts than Texas or Georgia, he was well positioned to do this after he sewed up the GOP primary. (I'd argue that the primary was basically won once Rick Perry, his last real challenger, dropped out at the beginning of the year--but at the very least Romney had this thing in April). At that point, the party's right wing was already geared up to vote out Obama and would have backed a houseplant if that were their best chance of doing so.
Around that time, I'd suggested Mitt have a "Sister Souljah" moment, taking some public stance that would be seen as "brave" by breaking with his party's partisans--for example, by unequivocally condemning right wing media star Rush Limbaugh's nasty statements about Sandra Fluke (who Limbaugh made into a martyr-star). Romney's "rebuke" was lukewarm and weak (something along the lines of "I wouldn't have used such language"), representing a missed opportunity. Another chance would have been taking a stance to Obama's left on a key social issue--perhaps condemning gay-bashing statements from the fever-swamp portions of the GOP, or prominently endorsing a sensible immigrant reform law like Marco Rubio's "mini-DREAM" act, or favoring increased access to medicinal marijuana.
The thing about these stances is that none of them are per se inconsistent with an overall message of smaller government and pro-business policies, which is the central message Romney is pushing (and won his primaries with--he was never going to out-gaybash Rick Santorum, even if he slaughtered a gay goat on an altar during one of the debates). But more importantly, it sends a signal to the very suburban moderate voters that the GOP needs--the signal being, don't worry, this guy is more like the Massachusetts moderate from ten years ago than some tool of his party's right wing. My own feeling is that Romney is actually more moderate and pragmatic than this campaign has let on, but his fear of a break with his party's base is a problem.
At this point, it's probably too late for Romney to change the game--under two months left and most voters have made up their minds. But there should be a long-term lesson here for the GOP--a party that cannot occupy the political middle is going to lose every time.