The 2004 presidential election produced a dramatic increase in voter turnout and in a variety of campaign activities beyond voting. In this article, we demonstrate that the main reason for this increased turnout and activism was the intense polarization of the American electorate over George W. Bush. George Bush in 2004 was the most polarizing presidential candidate in modern political history and a much more polarizing candidate than he had been four years earlier. Americans either loved him or hated him and they went to the polls in record numbers to express those feelings. Our findings do not support Morris Fiorina’s suggestion that polarization turns off voters and depresses turnout. Instead, they support the rational choice theory of turnout proposed by Anthony Downs: polarization energizes voters and stimulates participation. Whether turnout and activism remain at the levels seen in 2004 will depend on whether future presidential candidates produce a similar degree of polarization in the electorate.