Power in the USA is not concentrated on any one person or governing body. Instead there is a system of "checks and balances".
There are two main ways that this is implemented - through federalism and the separation of powers.
Federalism is the division of government between the national, state and local levels. The United States of America is a union of 50 states, each of which have their own legal standing and authority independent of the Federal Government.
The Federal US Government is based in Washington DC and is comprised of the President, US Congress (two houses - House of Representatives and the Senate) and the US Supreme Court.
There are 435 members of the House of Representatives. The number each state elects is dependent on its population.
There are 100 senators, two per state and nine members of the Supreme Court. Supreme Court judges are selected for life by the President and with the approval of the Senate. Each of the 50 individual states of the USA has its own Governor, State Congress and State Court.
Checks and balances refer to the separation of powers between the Executive (President), Legislature (Congress) and Judiciary (Supreme Court).
The framers (writers) of the American Constitution in 1789 went to great lengths to ensure that political power would not be concentrated within a single branch of national government.
The President nominates Ambassadors and members of the Cabinet, selects Federal judges and negotiates international treaties, but all are subject to approval by the Senate.
The Constitution specifies that only Congress has the power to declare war, but the President is Commander-in-Chief of the Armed Forces.