Several unique characteristics of our political system are listed below.

Popular consent is the idea that governments draw their powers from the governed.
Popular sovereignty is the right of the majority to govern themselves.
Majority rule holds that only those policies that collectively garner the consent of a majority of citizens will become law.
Individualism is the value and focus placed on individuals in our democracy and culture. Individualism holds that the primary function of government is to enable the individual to achieve his or her highest level of development. This makes the interests of the individual as important as or more important than those of the state. 
Equality is the idea that everyone is equal under the law.
Personal Liberty usually refers to individual freedoms. It initially referred to freedom from government interference; today it includes demands for freedom to engage in a variety of practices free from governmental discrimination.
Federalism refers to a political system in which power is shared among the various levels of government – in the case of the United States, the federal government and the states. Local governments are created by their states. 
Separation of Powers refers to the splitting of power between the legislative, executive, and judicial branches of government. This creates an intricate system of checks and balances.
Pluralism is a political model in which political power and resources are scattered so widely in our diverse democracy that no single group or individual can dominate or monopolize any substantial area of policy. Interest groups are a critical component of pluralism. An interest group is a collection of individuals organized to express attitudes or positions held in common in a effort to influence public policy.
Political Culture is a set of values, attitudes and beliefs that people hold about how political and economic life should be carried out.
Capitalism is considered to be an extension of individualism. Capitalism is an economic system that favors private control of business with minimal government interference and regulation in private industry.
Ideology refers to a specific course of action that people want government to take. Most of the population adheres to one of the four dominant ideologies in the United States: liberal, conservative, libertarian, and populist. It is a clash of ideologies that helps shape public policies in the political arena.
The Constitution is the ultimate written law of the land. It establishes the institutions of government and their powers, and specifies a wide range of civil liberties for citizens. The American political system is based on written law, all of which stems from the Constitution.
Rule of Law is closely related to the Constitution. Rule of law is the idea that we are governed by laws that are created in a democratic process rather than by the whims of kings or those in power. We elect officials such as presidents, mayors, city council members, members of Congress, as our representatives; they make and implement the law. As citizens, we obey the laws and abide by the rulings of courts and other administrative agencies. The rule of law allows due process and the right to appeal decisions. If a majority of citizens are unhappy with a law, democracy provides various ways to change it.

These characteristics appear in Jeffrey D. Greene, Public Administration in the New Century: A Concise Introduction (Belmont, CA: Wadsworth, 2005)