What it means that state politics are heavily nationalized

He mentions that the “R2” is 0.99 — a reference to a statistical measure called the correlation coefficient. That coefficient is described with the shorthand r; r-squared, the value shared by Abramowitz, is the coefficient of determination, measuring how closely the dots on that graph fit the displayed line. A value of 0.99 means, in essence, that they fit very, very well. The maximum value is 1.