Santorum is a politician, is again running for president and last week criticized a papal encyclical. He is also Catholic. The views he expressed are what they are, which is to say that rather than giving silent internal assent to a teaching of the Catholic Church he publicly opposed it. I see this as a test of discipline and obedience. Santorum failed.
Ideologues, whatever their political persuasion, view the world through a prism. This is why, for example, they typically seem unable to accept the teaching that both abortion and capital punishment are immoral. This holds true whatever the political persuasion.
But for Catholics, these are properly religious rather than political issues, and one either does or does not assent to the teachings of the Church.