Well, the 9/11 bombers were here on student visas. The first WTC center attacks in 1993 were done with tourist visas. Basically, all terrorists in the US in the last 20 years were allowed into this country legally. And, even if you close off the southern border, the northern border is still very open and unprotected. On the other hand, documenting who is here as a temporary worker has very real benefits to our government and society, so a lot of reward for a very small increase in risk.