The "Two-Party-Mentality" is a misnomer, not nearly as nuts as you might think.
We have a big filtering process in this country, concerning candidates. Did you see the Democratic candidate debate for President? We're 18 months away from that election, and 9 were in that debate. For the Republicans, 10 in their debates.
If Americans choose to pay attention, our political system works rather well. It's only when a huge portion of Americans becomes complacent - and not vigilant - that things political begin to skew at dangerous angles.
That's what you've seen over the last 6 years - the result of extremism in American politics. We're now engaged in getting some balance back, but it takes time. We Americans are getting very rudely reminded of what happens when we assume our political system "runs by itself".