When George W. Bush addressed the feverish swath of supporters on November 2, 2004, at the Ronald Reagan Building—just a stone’s throw from the White House—he had many people to thank for his successful re-election. Among them was Karl Rove, who Bush referred to as the “the architect.” While Bush was the man of the hour, Rove cemented his legacy as one of the most influential figures in U.S. politics for his tactical use of voter data.