All of these questions and more can be answered by this handy video I found, courtesy of YouTuber "Grey" in the series "Grey Explains Things."
There isn't one. That's the problem, not just with American politics, but politics in general. There are fourteen solutions to every issue, and all fourteen of them suck for someone out there, somewhere. It's all a matter of who has the power, because those with the power want things to suck for them as little as possible.
And what determines who has the power?