The most powerful person in the world is chosen by the U.S. presidential elections every four years. The United States of America is a world leader whose actions, to a degree, affect just about every other country in the world - so its elections are closely watched not just by U.S. citizens, but by people all over the globe. The results of presidential elections affect many outcomes: public policy, international relations, and the direction that the country takes in the following four years. But how exactly do presidential elections affect the stock market? And how has the stock market been used to predict the outcomes of future elections?