I am not familiar with a well known intent to take over America (by most American Moslems) and more importantly, I am not aware of any great risk that such an attempt can be successful.
Again, IF Moslems will become a disruptive element in our society, their emigration should be limited. At present I believe they are at most 1% of the population, therefore in no position to take over.
It's apparent that one doesn't need great numbers or have great difficulty in infiltrating the U.S. government with all those rules protecting religion and national origin. Once you infiltrate, then disruption is childsplay and the public can do little about it until the next election and even then one can't be sure the problem will be solved.