If Romney loses this election (I'm not ready to concede that as a fait accompli), a major reason (albeit not the only reason) will be the extreme right-wing policies of the Republican party.
Romney has several hurdles to overcome in his race against Obama. He is being held back by the Todd Akins and Richard Mourdocks of his own party who make idiotic comments about rape and God's will and women's bodies shutting down in cases of "legitimate" rape. He's being held back by the Michelle Bachmans and the Rick Santorums who are hell-bent to impose their strict moral and religious values on a voting bloc that doesn't share those values. And to some extent he's also being held back by the policy failures of the Bush administration.
Romney has been by no means a perfect candidate. He waited far too long to repudiate the attacks on his personal record, and he didn't hit Obama nearly hard enough on the current Benghazi scandal in the last debate. But the major problem for the Romney candidacy is that he was put in the very difficult position of having to convince the Tea Partiers that he was conservative enough to get the Republican nomination, and now that conservatism (faux that it may be) is unappealing to a large percentage of voters.