Who has the final say for what america does

In the final anaysis, the American voters do. This is supposed to be a representative form of government. The people elect representatives to pass laws, subject to the Constitution of the United States, judicial review by the Supreme Court, subject to veto by the president, etc. If "the people" are dissatified with any of these parts of the government, even the Constitution, they can be changed. Enough political pressure on just about any issue can cause it to go the way that most people in the country want it to go.

A good example is prohibition. Back in the old days enough people got together and pressed the notion that alcohol was bad for the general population and they pushed it so far that the Constitution was changed to ban it. Several years later, the public changed its mind and the Constitution was changed back to the way it originally was.

One major problem with this scenario is that many, many people do not vote or get involved in what their representatives are doing. They don't exercise their power over what government can do. Other people exercise their power over policy and we end up with policy being controlled by such factors as greed, self-interest and political whim.

Oddly enough, I had an essay test question on this very subject many years ago. I have a bachelors degree in government and politics.