While a challenger's presidential campaign can quickly adjust and adapt to shifting seas like a speedboat, an incumbent's campaign behaves more like a battleship, maneuvering slowly and making very large waves. Instead of a core inner circle calling the shots from a "war room," a president's re-election team must coordinate with White House staffers and the president's cabinet - all of whom have agendas difficult to change, control or coordinate.
The pivotal moments in incumbents' campaigns are policy moves that take months to plan before they're unveiled - and often just as long to see their effects. Challengers can make promises, but their talk is cheap. Everything an incumbent says or does has lasting consequences, and it is seldom clear whether the eventual payoff will justify the costs.
Samuel L. Popkin is the author of The Candidate: What It Takes to Win - and Hold - the White House [Oxford university Press, $27.95].