The most polarizing presidential contest in decades, and by far the most expensive at $1.2 billion, is expected to draw a record number of voters Tuesday -- an estimated 10 million more than took part in the split decision of 2000.
Worries about war in Iraq, doubts about the economy, and deep rifts over religion and culture have energized this national campaign like few others, according to politicians and analysts watching the race.
"This is the most contentious and divided electorate since 1968, when the nation was galvanized by racial unrest and the Vietnam protests," said Elizabeth Sanders, a presidential scholar at Cornell University.
Democratic challenger Sen. John F. Kerry appeared to be gaining ground and momentum on President Bush before Friday's release of a videotape of Osama bin Laden warning Americans of more terrorist attacks if the United States continues threatening the security of Muslims.
Al-Qaida's surprise election eve taunt hit both campaigns like a whirlwind in a pile of leaves. Bush and Kerry interpreted the tape to their advantage. But it reinforced the nation's wartime footing, pushing economic and other issues momentarily into the background.
"This is a substantial break for President Bush," said University at Buffalo analyst James E. Campbell, a conservative. "In the upper Midwest states, where economic issues are not as much in the forefront, this could tilt the election for the president."
"The polls show the president holds a double-digit advantage over Sen. Kerry in his handling of terrorism," Campbell said.
Bush stressed his role as a wartime president in the opening line of his radio address Saturday.
But in a speech in Wisconsin, another closely contested state, Kerry blamed Bush for allowing bin Laden to escape in late 2001 in the mountains on the Afghan-Pakistan border.
The Reuters/Zogby Tracking Poll gave Kerry a small edge over Bush and showed Kerry leading the Republican incumbent in four battleground states including Florida and Pennsylvania as of Saturday morning. Bush was ahead in bellwether Ohio.
A top Bush strategist, Matthew Dowd, conceded during the week that the Massachusetts senator's campaign was mounting a superior get-out-the-vote effort.
"I worked in the 2000 (Al) Gore campaign, and the passion and enthusiasm crowds are showing for John Kerry is unbelievable," said Michael Wholey, the man directing Kerry's foot soldiers.
Wholey said the Democrats recruited 250,000 volunteers to help get out the vote this year, compared to 90,000 who helped in the Gore campaign.
Dowd predicted a voter turnout of between 115 million and 120 million on Tuesday -- compared to 106 million in 2000.
Curtis Gans, who heads the nonpartisan Center for the American Electorate, estimated that 118 million to 121 million would come to the polls, with the higher number representing about 58 percent of eligible voters.
Such a turnout would set a numerical record but not a percentage one. The 1960 contest between Democrat John F. Kennedy and Republican Richard M. Nixon drew 63 percent of eligible voters to the polls.
There is no uncertainty about the expense of this race. Outside independent organizations are spending about $500 million on ads denouncing Kerry or Bush.
The presidential race will cost a record $1.2 billion when it is over, according to estimates by the Center for Responsive Politics.
Combined with the congressional races, spending on federal elections for this cycle will reach $3.9 billion -- a 30 percent increase over four years ago, the center said.
Despite widespread predictions the race will be so close it will wind up in the courts again, both sides predicted a victory so broad that it will be known Tuesday night.
In final week briefings, Bush aides seemed to be on the defensive; the Kerry camp was upbeat.
Bush campaign chairman Ken Mehlman, for example, made several references to attempted voter "fraud, intimidation and lawsuits" mounted by the Kerry campaign to steal the election.
Democratic pollster Mark Mellman said Friday that Kerry was already winning the election. Interviews and projections of early voting in Florida, New Mexico and Nevada, Mellman said, gave Kerry an advantage over Bush of between 5 and 12 percent.
Helping Kerry, Wholey said, was the high percentage of unmarried women who were newly registered voters for this election -- 34 percent.
Also boosting Kerry was the disappearance during October of the "security moms" who tended to support Bush. These were described in September by the Bush campaign as suburban mothers who backed the president because he would better protect their children.
Bush spokesmen said this phenomenon caused the customary gender preference for the Democrats to dissolve.
However, Debbie Walsh, director of the Center for American Women and Politics at Rutgers University, said "security moms" were "a kind of artificial construct."
Current polls, Walsh said, show women prefer Kerry to Bush 51 percent to 39 percent. The gender gap "fluctuated right after the Republican National Convention, but it never really disappeared," she said.
Kerry solidified his standing with women, Walsh said, by his support of an increase in the minimum wage and pay parity for women.
"Women tend to feel more economically vulnerable than men," she said.
But with bin Laden back in the news, neither side Saturday focused on the economy, which remains flat with third-quarter business growth well below forecasts because of rising oil prices and a swelling trade deficit.
Looking back over the campaign, Cornell's Sanders said both candidates made parallel blunders: Bush by invading Iraq, and Kerry for supporting it.
Nathan Kelly, an expert on elections at the University at Buffalo, said Kerry stumbled by taking too long to respond to the attacks of the Swift Boat Veterans who charged that the Democrat falsified his Vietnam war record.
One of Bush's worst moves, Kelly said, was inviting Vice President Cheney to be his running mate again. Cheney is scorned by two-thirds of independent voters, Kelly said, "who don't really trust this fellow."
Mike Donilon, media coordinator for Kerry, said Bush's big mistake was spending too much time and money going negative on the Democratic candidate.
Bush's strategist Dowd said Kerry's error was spending too much time at the Democratic National Convention on his war record instead of laying out plans for the future.
New York's two most prominent politicians will spend today on the campaign trail. Sen. Hillary Rodham Clinton, D-N.Y., will campaign in churches in Newark, N.J., for Kerry. Republican Gov. George E. Pataki will be at Bush-Cheney rallies in New Jersey, Pennsylvania and Maine.
News Washington Bureau assistant Anna L. Miller contributed to this article.