The system does generally push towards a duopoly. Still there's more influence of voters inside the parties at the local levels than it seems at first. Many imp

The system does generally push towards a duopoly. Still there's more influence of voters inside the parties at the local levels than it seems at first. Many important issues are handled at the state level. There's more variation of the parties beliefs as well at that level. A Wyoming Republican can have fairly different views and priorities from a South Carolina Republican. Side note, personally I believe that the growth of the scope of the federal government reduces representation significantly. A big difference with China or Russia's one party systems is that the presidential candidates are chosen in primaries, which can have a large effect. Both Obama and Trump were relative outsiders who were able to win their parties primaries without being heads of their parties. To me the USA's executive branch system allows more choice in representative leadership than parliamentary systems where the parties choose the prime minister.