Four years ago the media preached that evangelicals could never accept a Mormon nominee(I'll admit I had my qualms with some Christians when it came to Romeny; he was my first choice in 2008). But this is a case classic liberal projecting. Prothero was clearly banking on the Christian bigotry he was sure existed to reject Romney. They're not living up(or down) to his caricature, so they're hypocrites.
This is a lot like President Obama's "that's not the real Mitt Romney" after the first debate. Fox News has more on this here.