Not hard, just takes a while:
5 years as a "green-card" resident.
Don't break the law (much).
Learn some English.
Learn some history.
Pay $225.00
Take the Oath.
So, assuming these terrorists have been planning things for at least five years, there are probably citizens of the U.S. who are terrorists. Lovely.
So, why do people always distinguish between citizens and non-citizens when talking about "what to do with the middle easterners"? Any ideas?