This interactive graph published by the Pew Research Center, tells a couple of important stories about the political mood in the Untied States. Neither is a big surprise. One is that the parties are more polarized, especially among the politically active. The second is that the country as a whole is not polarized (though not coalescing around an ideological consensus either), and tends to be moving slightly left overall.
Matthew Dickinson at Politico has a good analysis.