system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the country approximately 50/50 when it comes to the political spectrum? Is it a coincidence that it's divided so evenly, or is it a statistical phenomenon?

Why is it a constant back and forth? I figured it should be like 70-30 or something, but that doesn't seem to be the case...
gpt
No, it's actually what you would expect with a two-party system. Imagine tomorrow that either societal attitudes changed or the Democrats changed their policies so that they suddenly had the firm support of 60% of the country. The Republicans, now realizing that they're now never going to win the presidency or control of Congress change *their* policies to appeal to more voters. The change is so successful that it gives them the support of 55% of the country. The Democrats make their own change in response to *that*, rinse and repeat until it stabilizes at 50%. That's essentially what's happened over the past 150 years.