You're not really disagreeing, though, since this is a red herring. I didn't say Americans are equally divided between the parties. I'm aware that roughly half the country hasn't voted in presidential elections for many decades, and that two-thirds don't vote in the other congressional elections. That's irrelevant to what I said about the two-party system. One of those two candidates will become president, regardless of how many Americans vote. Therefore, objectively, the chances are one out of two that either candidate will be president.

Of course, that simple calculation abstracts from the popularity of either leader, which needn't be exactly equal. Mind you, it's very odd that the results often end up so close because of the rural-urban split, the Electoral College, and with around half the population not voting (because of voter suppression, etc), leaving around a quarter of hardliners for either party and a sliver of independents in the middle. The results of the last two presidential elections are far closer than they should have been because the Republicans have been busy rigging the system to bring themselves back from the brink of irrelevancy.