This article is intriguing, even though I'm not sure I really believe it in total. But he makes a couple of interesting observations:
Most conservatives did show up on Election Day, but a significant number voted Democrat. Mr. Obama picked up one-third more conservative voters than Sen. John Kerry, at 20 percent. Self-identified conservatives in exit polling comprised 34 percent of voters in both 2004 and 2008, yet the number who called themselves Republican dropped from 37 percent to 32 percent. In an evenly split nation, the GOP losing 14 percent of its base overwhelmed almost everything else.
Two key right-leaning constituencies deserted Republicans: security moms and Catholics. Though the media has made the "gender gap" a household term, the more apt classification was a "marriage gap." Single women were heavily Democrat, and married women leaned Republican. "Security Moms" became the label for married mothers attracted to the hawkishness of the GOP.