Mitt Romney didn't take the bait, while Herman Cain and Newt Gingrich tried to defend their latter day McCarthyism:
There's a difference between the oath of office, where everyone takes an oath to defend the Constitution, and the sort of oath Cain and Gingrich are proposing, which singles out a single religious group as disloyal. No one is compelled to serve the government, if you don't want to take an oath to defend the Constitution you don't have to run for office or accept a cabinet or judicial appointment. But that Constitution explicitly states that there will be no religious test for public office.
Gingrich's campaign is imploding, and Cain is a longshot. However, by demanding that Muslims who might serve in their administration take a special oath, Gingrich and Cain have revealed themselves as fundamentally unprepared to take the oath of office as president of the United States. Ironic then, that they should spend so much time questioning the loyalty of others. Perhaps even odder is that in a party so committed to superficial constitutionalism, the refusal to accept one of the most basic tenets of the Constitution isn't regarded as an immediate disqualifier.
Quite the opposite really, as Paul Waldman points out:
So here you have it: Given the opportunity, Gingrich gives expression to the worst impulses, and Romney, oddly enough, gives expression to the best. But you might have noticed that it was Gingrich who got the applause.
That's really the bottom line isn't it? The Constitution is precious, but only in as much as it protects the rights of those who are members of the Tribe.