For this one, let's start with a good definition of "theocracy."

the·oc·ra·cy
a form of government in which God or a deity is recognized as the supreme civil ruler, the God's or deity's laws being interpreted by the ecclesiastical authorities.

Rick Santorum, who is a radically conservative, pre-Vatican II Roman Catholic, has said that birth control is "not okay," has argued that states should have the right to ban contraception, that the federal government should require schools to teach creationism, that both homosexuals and adulterers should be imprisoned, and that doctors who perform a legal medical procedure are criminals.

Now, I'm not sure who Lewis is referring to when he writes "people" in that tweet -- but I do think it's deeply ironic that someone like Santorum is expressing alarm about theocracy in Iran.