He is up 3 points from last weeks CNN poll (14%) to this weeks CNN poll (17%). Romney has gone down from 26, to 24, to 20 in the last 3 CNN polls and has faced no scandal or gaffes.
I have no interest in attacking Herman Cain, but I will question your methods. The MOE on the CNN poll is 6.5%. Cain may very well rally at some point in the next month, but any sane observer will agree that he is currently trending downwards.