Which is what people retort with when they don't have an intelligent rebuttal.
Or else the person asking the question isn't really asking a question but bullying and hectoring. Which was the case here. How do you respond to bullies?
Or the guy was calling Santorum's dumbass out?
He handled it better than he did in the debate, when he basically said he voted in favor of liberal things in order to take one for the (republican) team.
So when he answered it in the debate he not only accidentally exposed the truth that he votes liberally, but also that the republican party is a liberal one.