To compile this simple rmd model, you will need to have the dev version of ggplot2 installed. If you don't have it installed, the rmd file won't knit. To install:
library(devtools)
install_github("hadley/ggplot2")
This file should be self-contained. To download the latest polls from Real Clear Politics, run the model and generate the plot, simply open the .Rmd file in RStudio, make sure you have all the libraries at the top of the code chunk installed, and click "Knit HTML".
If you want to just produce the chart, you can copy out the code chunk into an R script and run it interactively.
Enjoy!