Separation of Powers in America
In the American form of government, the president is elected by the people to fulfill the role of the head of State, and the head of Government. Some European countries developed a parliamentary system with a prime minister to fulfill the role of the head of government while the monarch had the role of head of state, and kept that type of government even after monarchies died out, usually replacing the king/queen with an elected president (except for the United Kingdom which still has a queen).
In a parliamentary system, the head of government (the prime minister) is elected by the party that has the majority of control over the parliament (or by the parties that have formed the majority coalition), this ensures that the executive branch and the legislative branch are essentially one and the same. In the United States the head of government (the president) is basically elected by the citizens, not the party that has a majority in congress; and the legislative and executive branches are completely separated to create a series of check and balances to try and prevent tyranny from either side.
This separation of powers in the United States was created by the founders to prevent another monarch to rule over their country again. If the president had the complete support and control of the congress, then it would be easier for him/her to abuse their power and exercise whatever ideologies they want to impose on the country. The problem, however, is that it creates a lot of tension between the executive and legislative branches (especially if both branches are ruled by opposing political parties). This means that it’s often difficult for both the executive and legislative branches to reach an agreement on policies and laws for the country, and slows down the productivity of the government as a result of this.
People also often debate over the actual necessity of directly electing a president. In the United States it has been such an important part of the culture to do so, that it’s now considered one of the greatest privileges this country’s citizens enjoy, so that’s probably not going to change any time soon. But other western country’s (including Canada, Germany, Japan, and Sweden) have been successful in managing their respective countries with a parliamentary system. It can be argued that this type of government ensures that the government works more efficiently because there’s less conflict between the head of government and the legislators, and also ensures that the head of government will be qualified and have experience in government (because he/she would have had to be a legislator before being elected as prime minister).
Even though the parliamentary system does have checks and balances in place (the government can be dissolved by the rest of parliament) it allows large parties and coalitions to have a greater amount of control over state affairs. In the United States there are only two main parties, so if it were a parliamentary system the majority party in congress would always elect the head of state. This separation of powers is thus ensuring that neither the legislative branch or the executive branch abuse their powers and take control of the government. Even though it slows down the efficiency of the government, it ensures that each decision is carefully analyzed and reviewed by legislators, and the executive branch alike.