4,000,0000 repubs who showed up for McCain in 08 failed to show up for Romney in 12. Romney failed to secure the base.
Where are you getting this from? McCain got 59,948,323 votes in 2008. Romney got 60,931,767 in 2012. He improved on McCain's vote count by almost a million votes (983,444).
Moreover, we (Republicans) LOST seats in both houses of Congress in 2012, despite gerrymandering in 2010. If the generic congressional polling stays at its current numbers, we're on track to lose a good many more in 2014.
Because we're alienating potential voters for no defensible reason.
What the earlier poster said is, IMO, accurate. The electorate tends to break down along social policy lines, with diehard liberal viewpoints on social policy going reliably D, diehard conservative viewpoints on social policy going R, and the moderates in the middle trying to decide between the lesser of two evils. Those moderate folks tend, by and large, to be repelled by what they regard as extremist socially conservative policy statements.
Gay marriage is a good example of that. Regardless of our personal viewpoints on that issue, the polling makes it abundantly clear that public opinion at large has swung and continues to swing, decisively, towards acceptance. Meanwhile, we're busily inserting planks into the platform that vigorously denounce it. That's a recipe for persuading people not to vote R on election day.
The sooner we jettison the social stuff and get back to basics on the stuff that people agree on (fiscal discipline, etc.) the sooner we'll be back in power. Until then, we're arguably shooting ourselves in the collective feet.