From The American Mind:

We must remember that presidential elections are not a thing apart from the rest of our constitutional and political system. Our major political parties came into being, and exist today, for the primary purpose of capturing the presidency. Their structure follows the structure of the Constitution because the Constitution apportions electoral votes to the states and requires a majority of electoral votes to win. Each state has a minimum of three electoral votes, with the larger states having more in proportion to the number of seats to which they are entitled in the House of Representatives. The Electoral College, in short, is organized on precisely the same principle as the United States Congress, and for precisely the same reason. Neither institution recognizes population alone as the exclusive measuring rod for democratic legitimacy.