While referring to the two most definitive Presidential powers in the US, it shall be mentioned that Article 2 of the US Constitution provides an explicit listing of presidential powers. Besides the Constitutional source, Chapter 12 provides an extensive historical overview into the three branches of government and their correlation of powers.
First and most important, is to outline the fact that the President of the US exercises his activities within the limits of his executive powers. The dimension of the executive power allows a president to be a chief of the national security matters. What is rather remarkable in that context is the fact that the division of powers in the American government is given to the divided government, meaning that government exercises its activities under the control of White House. In fact, President possesses extensive veto powers, which often can block decisions taken by the Congress and the Senate.

In fact, as mentioned in chapter 12, the Presidency in the US has gone through the long and extensive evolutionary process. Debates regarding presidential powers were taking place since the late 18th century. In retrospect, the power over militia has gone through the long and lasting process, too. Currently, it could indeed be called as the defining power in the decision-making processes in the American government.

Given the fact that American Presidency is limited in the timing for exercising activities in the office, President is limited in his application of activities on the political ground. In fact, the two terms in the office, which can last ten years the most, are confirmed in the Twenty-second Amendment to the US Constitution.

No less important is to mention that President plays a huge communicative powers not only with his constituency but also with the governors from Senate and the House of Commons. In fact, the second most definitive power, which is also listed in the US Constitution refers to the State of the Union Clause. Historically, Presidential addresses took place since the time of cadence of Thomas Jefferson, such a matter for communication remains of the great importance these days, too. State of the Union Clause gives power to a President to address the flow of the political direction of his policies that are to take place annually. Currently, such practice is being exercised on the annual matter and represents a direct executive duty of the President in the US. The tradition that started with Thomas Jefferson addressing the Congress of the United States was historically followed by the speeches made by Woodrow Wilson, until after the procedure was modified. The current US President Barack Obama also uses the chance to address the Congress annually, with the particular amendments conveyed in the procedural matters, too. The purpose for State of the Union addresses not only defines the polital direction of the office for the upcoming political season but also provides a possibility to install closer negotiations and exercise of activities between the three branches of government. Ultimately, the procedure is to reach on policies, which are commonly referred to foreign powers, legislation, and public deliberation. Therefore, one shall not underestimate that aspect of exercising Presidential duties.

Overall, it shall be summarized that President acts within the powers, written down in the US Constitution, which were modified in the historical context, and extended or limited his activities. These days, the President of the US carries out executive powers with the ultimate control of the military and national security matters. Besides that, the coordination of activities between the three branches of government is being completed through the State of the Union class, which are no less important for understanding the context of political activities.