First we had Romney vs. Trump, then Romney vs. Bachmann, then Romney vs. Perry, and now we have Romney vs. Cain. Remember Joe Louis' Bum of the Month club? That's what the Republican primary campaign looks like this year.
The problem with Herman Cain, of course, is basically the same as the problem with Donald Trump: He knows how to stir the troops, but the whole campaign is basically a joke to him—and even tea partiers aren't going to stick with a guy who treats the presidency like a joke. The zingers are all great, but if you want to be the leader of the free world you can't perform stupid burlesque about not knowing anything about Uzbeki-beki-beki-stan; if you want to run the economy you can't build your whole campaign around a corporate slogan like 9/9/9 that even the marks know is ridiculous; and if you want to be commander-in-chief you can't transparently not care about foreign policy. It's all fun for a while, but it wears thin pretty quickly when it becomes clear you're really campaigning to get a Fox News show, not to sit in the Oval Office.
Anyway, to show this graphically, I've helpfully extended the latest poll of polls from Real Clear Politics. Perry might do a little better than I'm predicting, but not much. As for Cain, he better enjoy his moment as Mitt Romney's latest bum. It won't last much longer.