Maybe a small party will not make it to the presidency because of the issues you have mentioned (to that also add electoral trickery like gerrymandering). But

Maybe a small party will not make it to the presidency because of the issues you have mentioned (to that also add electoral trickery like gerrymandering). But there are many branches of government that can help influence government, and you can also run for office within your state. Here some states have independent senators. In China you don't really have independent branches of government, it's just the Chairman of the party and whatever he wants is what gets done.