Does anyone have good resources for what exactly each role of the United States Government is supposed to do? I understand the constitution is a framework, I am referring to resources that are well sourced and ideally not from the last 100 years or if they are then perhaps not something that is propaganda filled.

I am trying to understand what is the purpose, authority, and capabilities of the different roles in the US government from the top down specifically. A history of when new powers where granted or old powers removed would also be helpful. The last 100 years would of course be included in anything historical.

I am trying to get an understanding for where we started and where we are from a "job description" type perspective.

Thanks in advanced.