The next plot shows how all the GOP field fares against Obama, highlighting each candidate in turn. Points above the diagonal line are polls in which a Republican was ahead of Obama, while points below the line reflect an Obama lead. The point here is to get a sense of the overall strength of the GOP field and how each candidate performs relative to that field (the gray dots) as well as relative to Obama. (The points have a few tenths of a percentage point of noise added so polls don’t overlap each other exactly. This means individual polls may not appear at exactly the same point across each panel. The highlighted red points, however, are not adjusted in this way.)
The plot below shows how the GOP field has shifted in relation to Obama since June 2011. As the cloud of points moves up and to the left, Republicans do better as a group vs. Obama. As the points shift down and to the right, Obama gains the advantage. The points above the diagonal are polls show one or more Republicans holding a lead over Obama in polling that month.