The Muslim Brotherhood, The N.O.I., and every Mosque in this country has lots of eyes on it.
I think we need to draw a distinction between their intentions and reality.
The reality is, these types of groups will never, ever, ever turn America into a Muslim society. Ever. Just to be clear, I mean never. We ain't Europe, we ain't Indonesia, and the Christian roots of this country run so deep it will never happen without a bloodbath, and even then it wouldn't happen. Athiests have been trying for decades through aggressive court action to de-Christianize the U.S., and all they really have managed to do is be a pain in the arse by removing revered symbols. Yes, there is a war on Christianity be waged by the left. The very reason the left is becoming more shrill, however, is because they are losing the substantive parts of it. They are losing the argument on abortion, Darwinist dogma (as opposed to objective biology) is seriously being questioned by open-minded scholars, you hardly ever hear a democratic dare use the term "religious right" anymore, and Christianity is spreading throughout the world at unprecedented rates.
The intentions of groups like these, however, have to be exposed, and exposed repeatedly. Just because America will never become an islamic society doesn't mean we should coddle subversive groups with such goals in our midst, and it doesn't mean we should start accomodating islam the way the left would love us to. Groups such as the Brotherhood are natural facilitators for international terrorism, and politically their members are certain to be backing pernicious policies designed to undermine our traditions and values. Islam is, quite frankly, not compatible with western democracy. If someone can show me an example that proves me wrong, I'd like to see it. Turkey knows it, that's why military recruits have to undergo what is literally a "deprogramming" regimen to remove the islamic worldview from the heads of their soldiers, lest the country would turn into another Iran.
My point is, don't get scared. Get mad. Fight the influence of such movements at every turn. Not because they might succeed, but rather to let them and others know they are foolish to even try.