He graphed the poll numbers -- both of national and state polls -- of the last six weeks for the different candidates.
Here is Mitt Romney's graph:
(For those who are subscribed to the blog, you will have to click on the link to go to the actual website to see the graphs.)
If Mr. Romney and Mr. Cain are on a somewhat downward trajectory, you’d expect to see another candidate gaining ground. And that candidate is, indeed, Newt Gingrich. He’s polling in the mid- to high teens in most recent surveys, with occasional forays into the 20s. Also, for whatever reason, his state-by-state polls have generally been better than his national polls, so if anything the national surveys may somewhat understate his momentum. This method now shows him at about 18 or 19 percent of the vote, meaning that he’s roughly tied with Mitt Romney.