Like oil and (holy) water

The thing you don't realize when you're younger is that the things you do/say will most likely come back to haunt you in a few years.  No one discovers this faster than a politician running for president.

About a month ago, a clip of presidential hopeful Rick Santorum in 2008 was discovered.  In it, Santorum was asked about Christianity and liberalism.  He said that there is no such thing as someone who is liberal and Christian. "You’re a liberal something, but you’re not a Christian," he said.

So I started to think about this in light of everything going on in politics right now.  When Rush Limbaugh is calling a law student a slut because she stands up for women's rights, where is the line?  Is there a line?  And most importantly, is Santorum right and we're all just kidding ourselves?  Is liberalism the oil to Christianity's (holy) water?