I'd posted an earlier version of this a few months ago. Slate has prepared an actual animated horse race, showing how the various GOP presidential candidates are doing in the polls over time. It's absolutely fascinating to watch. They have one for Iowa, and one nationally. What's clear in each is that Romney has a solid base, more so than the other candidates, that doesn't fluctuate much, while the other candidates, one by one, surge and then sputter out. It seems clear from the video that the rest of the GOP, the majority of the GOP, is desperately seeking anyone but Romney.
Here's the Iowa animation.
And here's the the national polls.