The recent survey by Pew (http://www.people-press.org/2014/06/12/political-polarization-in-the-american-public/) has folks wondering about the direction U.S> Politics is taking. America has a very moderate political tradition. It embodies an institutional and historical rejection of European party politics. During the Founding Era, James Madison wrote his celebrated Federalist 10 in which he lamented the evils of faction. Alas, they are necessary to politics and include the notion of political parties. (Madison later acknowledged the necessity of political parties).
But, the American political system is designed to make it difficult for third or minor parties to succeed. In recent decades we have seen independent presidential candidates such as John Anderson and Ross Perot rise and fall. The winner-take all electoral system is designed to defeat small ideological parties because it is nearly impossible for them to win.
Some scholars celebrate this. It prevents the proliferation of narrow, ideologically distinct political parties (such as those that might spring from right-wing movements like the Tea Party) and forces such movements to join the ranks of the two larger parties, moderate their views and form successful governing coalitions under the umbrella of the Democrats or Republicans.
Unfortunately, there is no doubt that the major parties have atrophied as a result of the lack of true challenges outside of the duopoly they operate. Campaign finance laws favor the major parties. Legislative and congressional districts are gerrymandered to ensure that only Democrats or Republicans can win. And, the winner take all electoral system dooms third parties to failure in the long run.
We could change all this. American cites use and experiment with alternative electoral systems that enable small parties to grow. Europe has had multiparty systems for some time and European democracy flourishes.
Alas, as we have seen in the wake of the defeat of Eric Cantor, as soon as the major parties perceive a threat to their duopoly, they can look to close ranks (or, in this case, the nomination process) to prevent small parties from gaining power. Ironically, in the land of the free market, the political marketplace has the highest barriers to entry.