A new Gallup poll finds Mitt Romney barely leading Herman Cain for the GOP presidential nomination, 20% to 18%, with Rick Perry at 15%, Ron Paul at 8%, Newt Gingrich at 7% and Michele Bachmann at 5%. The Republicans usually don't have an actually competitive primary race. Usually, at this point in the election calendar, the national polls show the eventual nominee leading the race by 20 or more points. So Romney is weak, and a new ad by the Perry camp will really hurt....