Without a true parliamentary system or ranked choice voting, there will always be a 2-party system. It's an unavoidable feature of our voting and legislative system. And both parties benefit from keeping it as a 2-party system and will never support legislation that changes it. It would require a fundamental change that I support, but is politically impossible for the foreseeable future.
In the meantime, supporting third parties I agree with results in wars of choice and gestapo. So I instead support candidates as nominees for the party that is less harmful.
Changing the 2-party system is essentially impossible. Changing the parties themselves is easy. Look at how much worse the GOP managed to get in just the last 20 years.