The two-party system endures through a combination of residual political loyalty, entropy and, most significantly, a set of legal and electoral structures that create extraordinary barriers for potential third parties or independent bids for office, rather than because it is a rational organization of political interests. Rules making ballot access for independent candidacies difficult, the challenges independent candidates face getting media coverage or even participating in debates and state and primary elections that are paid for, in substantial part, by the states rather than the parties all contribute to the dominance of the two party system. Blurring the line between state and party has been a problem of authoritarian regimes for decades. In the US, the phenomena is slightly different, but line between the state and the two major parties is frequently difficult to identify.
The growing possibility of another Clinton-Bush race is also something that reflects significant problems with our democracy. In most other countries, the spouse of a former president running against the son and brother of another former president would be prima facie viewed as evidence of structural problems with the country and probably widespread corruption as well. This election will not be seen that way because, well Hillary Clinton is beloved by many Democrats, and Bush can become beloved by many Republicans if he is seen as the guy who can beat Clinton. It is probably, however, worth taking a closer a look about what a Clinton-Bush matchup tells us about about our democracy.
The difference between the Tea Party and the rest of the Republican Party is minor and more a matter of style than substance. This is not a division based on big picture policy differences in which, for example, the mainstream Republicans understand that seeking to slightly raise taxes on the wealthy does not make somebody a socialist or that income inequality should be a concern to all policy makers interested in stewarding the economy towards prosperity. Moreover, mainstream Republicans have been alarmingly reserved over the last five years in their reactions to the often offensive statements made by some in the Tea Party movement.