Most presidential elections are character- or theme-driven. This one was event driven. That's what happens in wartime. You can spin all the theories you want about how Abraham Lincoln won re-election in 1864, but if Sherman had not taken Atlanta, Lincoln would have lost.
In the election of 2004, events were once again in the saddle. Given how Bush's term started, the election should never have been close. After 9/11 and America's swift crushing of the Taliban, President Bush had the political world at his feet. Over the next few years, he could easily have coasted to victory, crowning his achievement with the equally astonishing establishment of a democratic and pro-American government in Afghanistan just weeks before his own re-election. He would have won in a landslide.
Instead, and against all personal political calculation, Bush wagered it all on Iraq and nearly lost his presidency. The 2004 election hinged on Iraq, in three political incarnations: Iraq, the war; Iraq, the first presidential debate; Iraq, the media magnet for countless bad news stories. Together they very nearly overthrew Bush.
It certainly was not John Kerry doing the overthrowing. The only reason it was tight is that the Democrats picked a candidate singularly weak on Iraq. Kerry reflected precisely their own ambivalence. He could never articulate a consistent and coherent alternative policy. The entire Democratic Convention was an exercise in avoiding the issue. Kerry spent four days talking not about Iraq but about Vietnam. This glaring non sequitur gave Kerry the distinction of having a convention with no bounce. Even worse, by gratuitously bringing up Vietnam, a still bleeding psychic wound, Kerry opened himself to weeks of politically damaging attack from embittered fellow swift-boat veterans.
By mid-September the challenger should have been far ahead. For months the war news had been devastating for the President: the mounting casualties, the absence of WMD, Abu Ghraib, the kidnappings and beheadings. The President's popularity, once 90%, began to dip below the fatal 50% mark. Yet Kerry could do nothing. If the election had been held Sept. 29, it would have been a Bush landslide.
Enter Iraq in its second incarnation, the foreign policy debate of Sept. 30, and Kerry was reprieved. This debate, devoted overwhelmingly to Iraq, was a calamity for the President. Kerry held to two declarations--I really had only one position on Iraq, and I have a plan on how to win it--that went unchallenged by a confused and agitated President. Those 90 minutes undid months of advertising (abetted by Kerry's numberless about-faces) that had portrayed Kerry as inconsistent, cynical, weak and uncertain.
It was the President who looked weak and uncertain. Kerry, looking presidential, instantly passed the "Commander in Chief" threshold, just as John Kennedy had in his 1960 debates. The President's enormous lead collapsed.