He also ran a very anti-science campaign, alienating anyone who felt strongly about the possible dangers of climate change and the need for a strong space program, and lampooned Newt Gingrich, a member of his own party when he proposed a vigorous space program, violating Reagan’s dictum of speaking no ill of a Republican, while simultaneously backing away from the strategy of technology long advocated and followed by the Republican party by Jerry Pournell et al. while simultaneously and schizophrenically proposing to go back to a NASA-centric anti-small business space program. This helped alienate engineers, and non-social conservative intellectuals.
The 47% comment and his anti-illegal immigrant positions “self deportation, &etc.” further poisoned the well of public opinion among those older and retired voters receiving government assistance and among Latinos, while his anti-libertarian disrespect of Ron Paul and his supporters cost him valuable support among the libertarian and youthful wing of the Republican party.
In short he alienated every potential base of support the party needed in the future, while simultaneously embracing far right social conservatives that make others in the party and the general electorate (pro-choice, gay, or people with gay family members) uncomfortable.
I'm not even going to get into his lack of specifics on taxes, the economy and serious health care reform.