The presidential systems have for basis the clear separation of power between executive and legislative branches as we can notice in US and some Latin American countries. There, Presidents are not only the head of government but also the head of State. They are directly voted by the people in the US. He chooses Cabinet from outside of the legislature .Legislature has no effect on executive branch and vice-versa. Legislature has to trust presidents because there is no way but impeachment process to get rid of them. Impeachment is very rare in US but happened twice. Andrew Johnson and Bill Clinton were the first presidents’ impeached. This dispersion of powers in US, opposite the legislature to the executive power; moreover when these parties are rivals. Some statistics show that this happens 40 % of the time. US adopted presidential system because they were afraid tyranny and absolutism. Contrary to other system, presidential systems are too slow; these can lead to blind-alley. For instance US government shut down in October for 2 weeks because the Republican dominated House of Representatives would not pass Obama's budget. They disagree about Obamacare and want it out of their budget. That is why, people such as John Locke sustain that legislative power is more basic and important than the executive.
Contrary to presidential systems, in parliamentary systems power is concentrated. There is no real head of state.Peole are nominated for the figure. Indeed, it is whether a monarch or a weak president. Power belongs to the Prime minister. Voters