It's hard to believe now, but there were people who worried that Jack Kennedy would be a tool of the Vatican. And there are certainly plenty of folks who think that a group of Jewish men in the Bush administration have put Israeli interests above American interests. Similar things have been said about Massachusetts governor and fellow Mormon, Mitt Romney.
Catholics and Jews don't scare me. And Mormons sure don't scare me. But I have to admit I get a bit nervous about Muslims. This is why. I could easily link to a dozen other similar articles. Islam is not the only religion with in which many adherents think of themselves as belonging to their faith community first and of their nation second. Mormons like myself might think the same way. But one of the Mormon articles of faith is: "We believe in being subject to kings, presidents, rulers, and magistrates, in obeying, honoring, and sustaining the law". I think the same is true for Judaism, Catholicism, etc. There is a strong tradition of obedience to earthly laws and authorities.
In Islam, on the other hand, there is a strong tradition of conflating religion and politics, and respecting only the law of God. Islamic tradition also enjoins Muslims to help other Muslims and forbids them to act in ways injurious to other Muslims. So when Muslims living in non-Muslim countries are asked to choose between their governments and their religion, they have powerful incentives to choose the latter.
This is why I think it's a great idea to have American schoolchildren recite the Pledge of Allegiance every day. And for immigrants and aspiring citizens to affirm loyalty to their new countries.
Promises matter, and we need to treat them seriously. Maybe it's time for us to be a little less blase about letting people stay in this country who would like to overthrow its laws.