Selfishness
Sure,
It's pretty easy to look at the burgeoning masses and see that selfishness and income a a large determiner in party affiliation. The poor want more money and want the rich to be looted or government to provide more services (same difference). So their party promises them just that - appealing to their selfishness. The right want to hold on to as much of their money as they can and so the right promises lower taxes and less government (same difference).
Selfishness is a universal human trait. It comes in various flavors, sizes and denominations, but it is always present in one form or another.
;-)