It doesn't have to happen "in secret" in the U.S. They can practice their religion right out in the open! The U.S. is full of ethnic and/or religious communities. BUT, for the Islamic faithful to take over the U.S. and impose their beliefs and Sharia law upon the Americans would be unconstitutional, and that is what I was referring to. Unless they become the majority in the U.S., and simply because of the very behavior you mention, they will probably remain in small groups in communities - rather than in positions of power.
Unfortunately for the law-abiding Muslims, the Jihad believers have ruined it for them.