> I am pretty sure if a third party became more powerful the two established parties would gang up on them quickly to make sure their nice, comfortable duopoly

> I am pretty sure if a third party became more powerful the two established parties would gang up on them quickly to make sure their nice, comfortable duopoly keeps all the power. It's also possible that that might happen without the intentionality or explicit coordination part. https://en.wikipedia.org/wiki/Duverger%27s_law https://en.wikipedia.org/wiki/Duverger%27s_law For example, the successful third party might supplant the role of one of the existing major parties, marginalizing it. https://en.wikipedia.org/wiki/Party_system#United_States https://en.wikipedia.org/wiki/Party_system#United_States