How exactly do you do a background check on somebody from another country, who may not even be using his "real" name? I bet even if they wanted to, FBI cannot do much about it, not with such lack of meaningful info and not when under pressure to work with such numbers.
But never fear, no matter who wins, McStain or Hillbama, there will be a giant amnesty. Then when you capture the gangbangers, you would not even be able to repatriate them. So, be ready to pay for more prisons.