In the most cases, the performances of the candidates simply tended to confirm voters' opinions at the time.
But this year, the three presidential debates, as well as one between the vice-presidential candidates, attracted not only worldwide media coverage but also the intense interest of American voters. Polls show the debates appear to have affected how Americans will vote.
Allan Lichtman is a professor of American political history at American University in Washington. He and other analysts have said Democratic challenger Kerry took advantage of the spotlight to explain his positions on Iraq, the war on terrorism, and the U.S. economy more clearly than he had before, while incumbent President George W. Bush often appeared irritable, impatient, and not in complete grasp of the facts.
"George Bush went into this election [campaign] with a significant structural advantage as a sitting president. He seemed, however, to dissipate some of that advantage with three subpar performances in these debates," Lichtman said. "I'm not saying these debates will turn the election to Kerry, but certainly being beaten by Kerry three debates in a row might erode some of the advantages that George Bush had at the start of the campaign."
Most national public-opinion polls show that Kerry benefited more from the debates. Before the first face-off, which took place on 30 September, Kerry trailed Bush by at least five percentage points, and by as many as 10 points in some surveys. Just after the debate, almost every poll showed the two men virtually even. And they remain that way three weeks later.
But after the intense focus on the debates, what can voters now expect from the candidates, with just over two weeks to go until the 2 November election?
Very little, Lichtman said. He complained that both Bush and Kerry are running heavily scripted campaigns to avoid any chance of alienating voters.
"So far, these have been very much consultant-run, poll-driven kinds of campaigns. But, if either candidate going into, say, the last couple of weeks thinks they are significantly far behind and need kind of a 'Hail Mary pass' at the end, they could do anything -- including even maybe talking straight to the American people," Lichtman said.
Dennis Johnson is the associate dean of the graduate school of political management at George Washington University in Washington. He agreed that, after the debates, American voters should expect both Bush and Kerry to behave cautiously.
Johnson told RFE/RL that this caution comes not only from a fear of making a last-minute mistake, but also because so many factors are beyond their control: "I think the candidates are at the mercy of some cataclysmic event, such as a terrorist attack or bad news in Iraq. But what the candidates are going to be doing -- barring some unforeseen circumstance out there -- the candidates are just going to be out there trying as hard as they can to get out the vote and get their message across in those states that are still competitive."
Johnson said one other fear is defining these last weeks of the campaign -- the fear of the unknown voter. Voter registration in the United States has increased this year, he said, but there is no way to gauge the political preferences of these newly registered voters.
"Of all these hundreds of thousands of people who are coming out [to register] in individual states, we don't really know who these people are and who they're going to vote for. We don't know if they're mostly Democrats or mostly Republicans. So I think that's going to be one of the really interesting, unknown factors about this race," Johnson said.
Johnson said the increased public interest in this presidential campaign is likely to mean greater voter turnout. He notes that roughly half of all registered voters participated in the U.S. presidential election in 2000, down from around 60 percent when John F. Kennedy defeated Richard Nixon in the 1960 presidential race.
This year, turnout is not predicted to be as great as it was 44 years ago, Johnson said. Only about 55 percent of registered voters are expected to cast ballots. But he said that is an improvement over more recent presidential elections, and a sign that perhaps American voters are becoming more engaged in politics.