I don't think we know that.
I suspect that may be true, but there are just as many and perhaps more people born in this country who have no loyalty to it than people who are foreign nationals.
Just because you are a citizen born in this country does not mean that you are a loyal American. And just because you were born in another country does not mean that you are not a loyal American.
Those who are "targeted" are the people who are calling or receiving phone calls from known terrorists or known supporters of terrorism.
I'm not going to deny that their may be a few Americans in the group especially after Jihad Johnnie.
It is true that all the 9/11 terrorists were foreign nationals though and there is still a wrecking crew of them left behind.
These are the scum that I most object to being given the name American.