The ratings reflect a sense of who has "juice" -- a demonstrated ability to elicit favorable attention from critical sectors of the political world, including activists, major fundraisers, and member of the news media who are paying minute daily attention to what has become the earliest and most intense presidential campaign ever at this stage.
Some other points:
First, these ratings are geometric, not arithmetic. Say, for example, that Syracuse is the number one-ranked team nationally in men's basketball, the University of North Carolina is second, and Virginia is third. That doesn't necessarily mean that the gap between Syracuse and North Carolina is the same as the gap between North Carolina and Virginia. The top-rated team might be head and shoulders above the rest of the field, but in the ratings, they still are only one "point" better than number two. Shockingly, that makes these ratings slightly less mathematically rigorous than they might otherwise be. And some candidates might be strong in many categories, but so weak in others as to be potentially disqualifying. For instance, Rudy Giuliani ranks fourth overall, but his views on some social issues make him a long-shot in the eyes of many observers.
Second, we throw the following time dimensions into one blender to come up with the overall ratings: how the candidate has performed over the long haul to date; how the candidate is doing currently; and what potential the candidate has shown, based on everything we've seen so far, to excel in the future.
So, the numbers measure past, present, and future simultaneously.
Third, while there is an inherently subjective element to this, we don't just make this stuff up on hunches. We talk with a broad variety of sources in making our judgments: Washington savants of both parties, real-life activists in real states, interest group chieftains, and strategists for the candidates themselves.
Fourth, we think it is healthy to probe and measure the seekers for the world's most important job all the time, and not wait until the winter of 2008 to start asking questions. We are the Political Unit, not the Policy Unit, but suffice it to say that when the candidates start talking seriously about policy, we will divide our attention between horse race and substance.
With Sens. McCain and Clinton likely to hold onto their frontrunner slots for the foreseeable future, the Invisible Primary largely becomes about the other would-be candidates maneuvering to be viewed as the alternative to them, and about consolidating their positions so that if or when either pace setter falters, or decides not to run, the others can be ready to step into the vacuum.
And the possibility that either or both of the frontrunners ultimately decide not to make the race is real.
Despite the omnipresent reminder about how no sitting president or vice president is running for the first time since 1928, it is important to note that McCain, Clinton, Kerry, and Edwards have all been through at least one presidential campaign in a central manner.
All the other hopefuls will be having their first real exposure to what is quadrennially a very tough and unforgiving process.
It is a multi-dimensional process as well. McCain and Clinton are frontrunners because they are so strong in so many of the categories that make up the Invisible Primary Ratings.