Evangelicals are, in the main, hysterical hypocrites. The GOP can afford to lose them - because independents carry elections, not whining hypocrites.
You know what, snookums, everyone's a hypocrite. Get over it. Dangle someone over a volcano, you meet the real man.
If the GOP loses Evangelicals, they go the way of the Whigs. They are probably going the way of the Whigs anyway, having alienated people of color as thoroughly as they have.
("Hey, I've got a neat idea! Let's nominate a guy who belongs to a cult which thinks dark skin is a curse from God!" "Brilliant!" ) The Evangelicals have supported the GOP to the hilt and they've gotten very little for their troubles. Abortion is still legal, gay marriage is gaining, evolution is still being taught in the schools while prayer is banned. So let's slap them in the face by electing a cultist they hate.
what wins elections is enthusiasm. When I've been enthused with a candidate (Reagan, Bush-43) he wins. When I've been less than enthused, (Dole, McCain) he loses. Why? Because when I'm not enthused, I don't get out and campaign, I don't talk my indifferent friends into voting, I don't send money.
Romney is the first guy who will negatively encourage me against the GOP. And a lot of other people as well.
If Romney's the Nominee, I'll vote for Obama. I dislike the Mormon Cult that much. So does about 22% of the rest of the population. A lot more will discover they dislike Mormons when the Mainstream Media starts educating us about their whacky beliefs and crazy history.