As far as flailing, Cain is somewhat new to the crucible of the national media. Anyone will have their moments. Palin stumbled some as well a few years back.
I have heard some of the radio discussion make the point that a large number of Republican primary voters are very distrustful of the media which is why the polls are showing little effect. Also, it is a very well known fact that ANYONE can make sexual harassment allegations and even the false and weak allegations are hard to disprove. Without some evidence that Cain did something more than just make a comment, I have a feeling a lot of people will give him a pass.
As far as foreign policy, Obama had zero foreign policy experience as well. As I have said before, very very few Presidents have any prior foreign policy experience at all. If they guy is smart and has good ideas on other issues, he will likely do the same on foreign policy. At this time when domestic issues are paramount, I think foreign policy is way down on the list for most.