The law was amended in 2002 to authorize access by other federal agencies to NCES data for "investigation and prosecution of terrorism," which is broadly defined.
The only thing keeping Homeland Security away from your confidential Census Bureau data in the NCES' possession is the requirement that the Attorney General apply for a court order before it can access it. But the court's only function is to confirm the application shows "the information sought" is "relevant" to "investigating or prosecuting" a laundry list of federal offenses. This is a far lower standard than the test of probable cause required for criminal search warrants. Unless someone botches the application, the court's only real power is to verify it was signed.
The bottom line is that not much stands between Janet Napolitano and your confidential census data. Fortunately, you risk no more than a $100 fine for each question you do not answer; and it is unlikely you will be fined more than once. So the question to ask yourself is whether your privacy is worth $100--or whether the Census should be reformed to ask the only question the U.S. Constitution actually authorizes: "How many people reside in your household?"
Nick Dranias holds the Goldwater Institute Clarence J. and Katherine P. Duncan chair for constitutional government and is the director of the Institute's Dorothy D. and Joseph A. Moller Center for Constitutional Government.