Elections do matter, of course, because presidents make key decisions, especially about national security. Some elections matter a great deal. The 1800 fight between John Adams and Thomas Jefferson ended in the first transfer of national power from one party to the other. Sixty years later, Abraham Lincoln's victory prompted the secession of 11 Southern states, which in turn led to the Civil War. These elections shaped our national identity and profoundly influenced our political culture.
Most presidential elections aren't like that, however. The selection of candidates seldom entails a choice between radically different world futures. True, today's competitors campaign on big topics, including what will happen to social safety-net programs, such as Medicare. But the possibility that this election will pivot the country in a radically new direction is not as great as voters may think.
A president is not a monarch with unlimited power. The authority of the office is subject to the constitutional checks of federalism (sharing power with the states), bicameralism (the two houses of Congress), and the separation of powers between the executive, judicial, and legislative branches.
Presidents and their supporters feel these constraints very quickly. When Ronald Reagan won the presidency, conservatives hoped that he would shrink the federal government by scrapping the Departments of Energy and Education, among others. Facing a Democratic House, he could do no such thing, and those departments are with us 32 years later.