From the perspective of someone who is extremely pessimistic about the prospects of the US' democratic system to successfully guide it past the demographic and economic challenges on the horizon, hearing about how highly polarized politics has become--as if compromising between the Ryan and Obama budget plans like the country would have in the past is all the US needs to do to get its house in order--elicits little more than an eye roll.
But I realize that perspective is an outlier's. Divergence in political orientation really has steadily occurred in the US over the past several decades. Democrats have become more liberal and Republicans more conservative, as the proceeding graph indicates. The y-axis shows the mean political orientation score for each political grouping. The question on political orientation is on a 7-point scale. The higher the score, the more conservative the group is, with 4 as the mid-point indicating perfect moderation:
As someone with a cursory understanding of US history in the second half of the 20th century, my first reaction is that Southern Democrats becoming Reagan Democrats and eventually Republicans might explain the apparent polarization. As conservative Democrats have become disenchanted by the Democratic party's increasing focus on 'civil rights' and a corresponding diminution of bread and butter issues the working class cares most about, they've gone from calling themselves Democrats to calling themselves Republicans without really changing their outlooks and sentiments much.
That may be part of the story, and it's a phenomenon not entirely contained in the South even if more pronounced there than elsewhere, but it's not the whole thing, nor does it even look to be particularly significant. The same graph as above, this time with Southerners* excluded:
There aren't any detectable differences between what we get when Southerners are included or when they're excluded. Political polarization has been occurring nationwide.
GSS variables used: POLVIEWS, PARTYID(0-1)(3)(5-6), REGION(1-4, 8-9), YEAR
* Those living in the West South Central, East South Central, and South Atlantic Census divisions.