During the American Civil War General Grant's past history of "immoral behavior" nearly kept him from being commissioned and placed into action... as the war dragged on a *lot* of innuendo and rumors about General Grant's past and whispered present cropped up after setbacks with an aim towards getting him to quit or be removed... Lincoln, when asked to get rid of Grant, said something to the effect "I can't spare this man, he fights".
Eventually Lincoln brought Grant from his successes in the Western theater of the war to the Potomac and Grant did the job of eventually ending the war as a Victory for the United States. It was a job the political Generals of the old establishment just could not get done for lack of nerve/being outmaneuvered/being outfought/blundering/not being inclined to do what was needed etc.
Grant was not perfect. Far from it. But he was the right man for the job at hand and he got the job done.
Cain is turning out to be a fighter. In the end I suspect Gingrich and Romney would have their own failures for their own reasons that their detractors can readily provide. Perry is a question mark. Cain at least is fighting and saying he won't quit because of the standard "lets make a scandal so the scary Republican quits" meme that both sides pull out against unwanted candidate.
I like Cain more and more.