The North-South divide that goes back to Lincoln's time, and has never been resolved. On one side is the extreme right in the form of the NRA, and on the other side are moderates in the form of the Bloomberg-Giffords-Kelly group.
North Carolina, Virginia, and Florida are now purple states. 2013, 2014, 2015 & 2016 will be key years to see who controls these states.
Demographics are changing in favor of non-whites. Women are taking control because they are smater and have more education.