For most of the year, both campaigns have operated under the assumption that whoever wins two of the big three battlegrounds - Florida, Ohio, and Pennsylvania - will win the White House.
But as the candidates hurtle across the country in their final full week of campaigning, they are paying just as much attention to a group of smaller states, whose electoral votes could now prove decisive in what looks to be an exceedingly tight race.
The reason for this is simple math: If Sen. John Kerry holds Pennsylvania and wins Ohio but loses both Wisconsin and Iowa, he would ultimately still fall behind President Bush in the electoral vote count. If Kerry can hang onto Wisconsin under that same scenario, it would put him over the top - unless he fails to hold New Mexico. But if he takes New Hampshire, New Mexico won't matter.
Similarly, if Bush wins Florida and Ohio but loses Nevada and Colorado, he'd come up short. Or, if he were to win the two bigger states but lose Nevada and New Hampshire, he and Kerry would wind up tied - throwing the election to the House of Representatives.
Of course, Florida, Ohio, and Pennsylvania remain critical - and sweeping all three would hand either candidate the election. But while Kerry probably does need to win two of the three to get to 270 electoral votes, it wouldn't be a lock, since Bush could map out a win with only Florida or Ohio, by stealing some of the smaller states from Kerry's column.
"It's pretty hard to come by a scenario whereby Kerry loses both Ohio and Florida and wins the election," says Alan Abramowitz, a political scientist at Emory University. "But it's a little more likely for Bush to be able to lose two of them and still win."
The increasing importance of every electoral vote reflects just how tight the race appears to be in the final days, with the electoral map looking just as narrowly divided as in 2000. Most of that election's closest states appear to be once again coming down to a handful of votes, meaning the smallest shift could push either candidate over the top.
Interestingly, while Bush has clung to a narrow lead in most national polls, Kerry is running slightly ahead in polls that separate out battleground states.
The discrepancy between those two results, seen across a number of recent public polls, may or may not prove lasting or meaningful. Analysts say it may reflect the fact that Bush is drawing stronger levels of support overall from red states than Kerry is from blue states, with his base more consolidated than Kerry's. But it could also reflect the fact that Kerry is slightly ahead in some of the bigger battlegrounds - states like Pennsylvania - while the smaller states are increasingly the most closely contested.
Searching for any kind of edge, the candidates are barnstorming the country this week with high-wattage surrogates - former President Bill Clinton for Kerry, California Gov. Arnold Schwarzenegger for Bush - and pressing their closing themes. Bush is zeroing in on the war on terrorism, planning a final ad and a speech that aides say will address the subject in a more personal way; Kerry is balancing security and domestic issues, saying Americans want a president who can defend the country and fight for the middle class.
Both men are battling for the remaining undecided voters, who, if they break decisively for one candidate, could still hand the winner a sizable electoral mandate. But more important at this point, analysts say, is getting core supporters to the polls.
"We're going to go down to the wire here with a very close election," says Democratic strategist Bill Carrick. "It's going to be all [about] turnout."
A belief in the strength of their ground game is one reason Kerry's campaign has sounded increasingly confident about states like Ohio. The Democratic turnout operation there, fueled by third-party groups such as America Coming Together, is "unprecedented," Kerry strategist Tad Devine told reporters. "It's going to favor us in the end perhaps by two or three points, which, in a race where we think we're ahead, is of tremendous significance."
Kerry advisers also say Ohio's still- lagging economy and a jobless rate that remains higher than the national average have made the state increasingly difficult territory for Bush - who, they note, did not visit Ohio for 20 straight days this month, though he's scheduled to campaign there Wednesday.
But several states in the upper Midwest - Wisconsin, Iowa, and even Minnesota - are looking tighter for Kerry, as is New Mexico. Al Gore won all these states by exceedingly close margins, and Bush has visited them repeatedly over the course of his presidency. The economy has been better in most of those states, and Bush aides believe their cultural conservatism may benefit the president. And while no single one of these states can match Ohio's electoral value, winning just two of them - say, Wisconsin and Minnesota - could make up for the loss of the Buckeye State for Bush.
The biggest wild card remains Florida - which, once again, could wind up as the most important state. A fast-changing population - including a surge in non-Cuban Hispanics, retirees, and young workers - makes the state one of the hardest to track politically from cycle to cycle. Gov. Jeb Bush, the president's brother, remains popular, and Florida's economy has been relatively strong. But the impact of four hurricanes over the summer remains unclear, particularly since the hurricanes hit in GOP-dominated areas. Democrats note that the state was basically distracted throughout the months of August and September, when Kerry was being pummeled by attacks on his Vietnam record, and Bush experienced his biggest lead of the race, following the Republican Convention.