In the old series "Lucy", she goes into a small town hotel where the owner is the doorman, mayor, and ultimately cop, judge and sheriff. The results are funny on TV but disastrous in real life, when folks are allowed to go outside their swimlanes.
We've made our executive way too powerful. On this score the far right is almost right -- though they have no problem with such power when they are in power. The once powerful Congress has delegated much of it's power to the executive in such a way that it is more an obstacle and nuisance sometimes than a constructive part of the legislative process. Our legislators, especially but not exclusively the Senate, are both too powerful and too disconnected from their constituencies to be effective legislator. Our powerful interests like this because it makes it easier to buy influence through campaign bribes, but it not only is bad and corrupt government but bad process. Our general legislators depend on staffers who often work for the companies they plan to go too after doing their time in government, and they write legislation that always is highly influenced by, and sometimes directly comes from, the corporations and interests they are supposed to regulate.
The root of corruption doesn't come from the mere fact of corporate interest in government. That is natural. A system or commons develop when folks divide up property so that people can specialize and do what they do best. Corruption comes from folks trying to "swim" outside their proper swimlane. Just because someone is good at one thing doesn't automatically mean they are competent at another. Worse the resulting conflict of interest can mean they are automatically going to be incompetent at the things that are outside the swimlane where their natural ability lies.
Too de-conflict these functions we would be best off if we setup institutions that involve the citizenry. What do AARP, NRA and other modern membership corporations have in common? The members have very little legislative power and very little say in the government of the organization that "represents" them. Thus the NRA is famous for being more about the companies that manufacture arms than about gun owners, and the AARP is sometimes accused of being in cahoots with insurance companies and others doing business with or through them. What we need are formal "Legislative Advisory" organizations that represent their members, are organized as "advisory" legislatures, and can do the work presently done by staffers --but would do it in a nationally integrated fashion from bottom up (Village, Town, City and County level on up). Their leaders would be elected, their memberships would meet in Assembly at the local level and as representatives at top levels. Groups like the AARP, Medical Associations, Unions etc.... organized this way would be powerful. And their recommendations for law and regulation would become law easier.
And we need a juridical function in most of our executive functions. But that is for another post.
The Japanese used to have layers of administration. They had an Emperor, who often was a front-man for an older "retired Emperor" who held more power than he did. And then they had a Shogun who was out-front and supposed to defend the country from invaders, but who in many cases had a front man himself and operated from behind a screen (often literally). In practice all these people would be conspiring to put the power completely in their own hands in many cases. But looking at it from a process point of view, there are good reasons to separate the roles. No man can safely (to the system) be both judge jury and executioner. This is the principle behind separation of powers. The Emperor was acting as Judge, or magistrate over the country as a whole. In the case of the imperial court he was both President and Supreme Court justice equivalent. The Younger person was usually given some part of that, often the judicial function. The Shogun had the executive function; and often the elder Shogun would act as executive judge, while the younger was the actual executive. This may seem byzantine, but the purpose was integral. It had integrity. As usual people in charge are the first ones to subvert their own roles so I'm not suggesting in any way we imitate the Bakufu or the Imperial Court. But what I suggesting is that separating the government into Executive, legislature and judiciary is not enough to enforce good government. On the contrary, we've given way too much power to the President.