This is what South Park does best, a totally random story based on something we know bothers a lot of people and ties into political satire which doesn't act as the main course.
This story seems to fall into place so naturally. Nothing seems forced or done for the sake of not having a better idea. You flow from start to finish savoring every moment and not wanting it to end.
Quite possibly the reason for this episodes success is it's well measured combination of Cartman and Randy; this story is the perfect storm to explore everything that makes those characters great. Throw in Butters and some brilliant Kyle jokes and this episode really does have everything that makes South Park great.
Maybe I'm slightly bias because the Tea Party Movement annoys me, but there's no denying they got ripped good and proper, and while saying people have small junk is hardly the apex of insult humour, it nevertheless did make a very valid point about 'why so angry?' and the fact that these attacks on Obama stem from the most trivial and mostly unfounded reasons. why not put it down to penis size haha!
Nevertheless I dont think it was too brutal on them and I think all men can relate to how paranoyed we can be about penis size, and if you have to complain then not only is that funny, but you are exactly the type of person this episode was ripping on and you need to get a grip!