What assumption about the executive department underlies the creation of independent regulatory commissions?
In the US, often times independent regulatory commissions are appointed to investigate various problems, or situations that may have problems. The Executive branch of the US government has many departments and are charged with investigating and regulating various areas. If there seems to be a problem of any kind, departments such as the Department of Justice, would almost with a doubt be called upon to investigate a situation where Federal laws perhaps have been broken or unfairly administered.If Congress believes that the Department itself may have violated any laws or violations, the assumption is that it would be impossible for the DOJ ( Dept of Justice ) to investigate itself. Thus in the Case of a time during the Clinton Administration, there may have been legal irregularities by the Chief Executive or the DOJ, it was prudent to appoint an independent prosecutor to perform the investigations.
The underlying assumption here, was that because the president appoints the US Attorney General who runs the DOJ, only an independent body can be trusted to investigate the situation.
The above is one example of this. Clearly the executive branch of the US government has numerous responsibilities. Problems within the executive branch are most often handled and investigated by the executive branch and may report its findings to Congress. However, in delicate or extremely important situations, an independent "commission" needs to be called on to perform unbiased investigations.