* Ohio is crucial, but several states could be kingmakers
* Obama a slight favorite in five of eight toss-up states
* Electoral math still favors Obama, but Romney is gaining
With one week left in the tight battle for the White House, it's all about the vital swing state of Ohio. Unless it's about Colorado - or Iowa, or tiny New Hampshire.
Democratic President Barack Obama and Republican challenger Mitt Romney both have clear paths to the 270 electoral votes needed for victory - and they don't all go through Ohio, the state that both sides have long viewed as key to capturing the White House.
Obama still has a slight electoral map advantage fueled by his slim lead in Ohio, but Romney has steadily closed the gap or moved slightly ahead in some other battleground states. Eight states remain relative toss-ups.
Both candidates can construct multiple winning scenarios, with or without Ohio. And it's now possible that the tipping point could emerge from another battleground, such as Colorado, where Obama and Romney are deadlocked in the polls.
"At this point, there are probably more electoral map scenarios than there are undecided voters," said Lee Miringoff, a pollster at Marist College, which is conducting surveys in key swing states.
"In a 50-50 race ... everything and everywhere is going to matter," he said.
National polls show the race is a virtual dead heat, but Obama still has a lead of at least 4 percentage points in states that account for 237 electoral votes, according to averages compiled by RealClearPolitics. Romney has a lead of at least that size in states that represent 201 electoral votes.
That gives Obama slightly more leeway in the fight for the remaining 95 electoral votes available in the eight toss-up states, all won by Obama in the 2008 election - Colorado (9 electoral votes), Florida (29), Iowa (6), Nevada (6), New Hampshire (4), Ohio (18), Virginia (13) and Wisconsin (10).
Obama is clinging to slight poll leads - which typically are less than the polls' margins of error - in five of those states with a combined 44 electoral votes: Ohio, Iowa, Nevada, New Hampshire and Wisconsin. That would be enough to put him over the top.
Even if he loses Ohio, Obama could still get to 270 electoral votes - and clinch the election - by winning Colorado instead. Obama won Colorado by 9 percentage points in 2008, aided by support from young and suburban voters and the growing Hispanic vote, but he is virtually tied with Romney there now.
Romney's path is tougher without Ohio, but still possible.
The former Massachusetts governor has a slight lead over Obama in Florida and has pulled even with the president in Virginia. If Romney sweeps those two states and adds Colorado, he would still need to win Iowa, New Hampshire and Wisconsin to capture the White House.
NEVADA SLIPPING AWAY FROM ROMNEY?
Of the eight toss-up states, Nevada appears the least competitive, with analysts and some strategists in both parties saying it is moving toward Obama.
An NBC/Wall Street Journal/Marist poll on Thursday gave Obama a 3-point edge in Nevada, and the last six public polls have shown Obama ahead.
Romney appears to have an advantage in Florida, where six of the last seven public polls have shown him with a small lead. RealClearPolitics puts Romney's average lead at 1.8 percentage points, within most polls' margin of error but symbolic of a trend toward the Republican, analysts say.
"Once an incumbent loses a grip on the race, it's very hard to get it back," said Florida-based pollster Brad Coker of Mason-Dixon. "Florida is gone for Obama, from what I'm seeing on the ground here. The map seems to be expanding for Romney and shrinking for Obama."
The multiple electoral scenarios have sparked speculation about alternative outcomes such as a 269-269 tie in electoral votes, which would leave the presidency to a vote by the Republican-led House of Representatives.
Another possibility: one candidate wins the nationwide popular vote, while the other wins the electoral vote - and walks away with the presidency.
The most heavily contested prize remains Ohio, and both campaigns are concentrating their time and resources there. Obama has an average lead in polls there of 1.9 percentage points, according to RealClearPolitics. Six of the last nine public polls showed Obama with a slight edge.
The other three showed a tie, including a poll released on Sunday by the Cincinnati Enquirer newspaper and the Ohio News Organization.
"The electoral map tilts slightly to Obama, but only because Ohio is so important and that's one state where he has kept a very small lead," said Thomas Riehle, a pollster at the market research firm YouGov, which also is surveying swing states.
"The polling is so much closer than it was in 2000 or any other close election year, so everything is hard to predict," he said.
'AN ILLUSION OF VOLATILITY'
Romney's poll gains since his strong performance in the first debate on Oct. 3 have been powered by growing voter confidence in his ability to handle the economy, an increase in his favorability ratings and gains among women and independents.
But Romney's early and mid-October momentum seems to have slowed or stopped since Obama's strong performances in the final two debates. National tracking polls have ebbed and flowed in a narrow range during the past week, with Romney keeping a slight lead in most.
But in a Reuters/Ipsos national online tracking poll on Sunday, Obama opened a slight lead on Romney, 49 percent to 46 percent, among likely voters.
On the state level, Romney's surge put him slightly ahead in Florida and Virginia, but has not been enough for him to overtake Obama in the Midwestern battlegrounds of Ohio, Iowa and Wisconsin.
Those three states alone, added to the states where Obama already has solid leads, would be enough for the president to win with 271 electoral votes.
"There is an illusion of volatility that is created when you have 90 public polls coming out every day," Obama senior adviser David Axelrod told reporters last week. "The fact of the matter is, this race has been remarkably stable over a long period of time."
Obama's support level falls short of the magic 50 percent mark in most national and swing state polls, a danger sign for an incumbent who is well known to voters and therefore could be unlikely to win the support of a majority of those who make late decisions.
The close race has put a premium on each campaign's ability to identify and turn out their voters, and Obama's camp has trumpeted its edge in early voting in swing states and its effort to get both frequent and sporadic voters to the polls.
It is unclear how Hurricane Sandy will affect early voting along the East Coast - particularly in Virginia. Bob McDonnell, Virginia's Republican governor and a Romney supporter, has vowed to extend early voting hours and restore power quickly to voting facilities in the event of outages.
Obama's Democrats have made early voting a focus of their campaign and represent a majority of those casting ballots before Election Day.
But Romney's campaign says early voting among Republicans in the toss-up states is running ahead of the party's pace in 2008, when Obama defeated Republican John McCain. In Ohio, Republicans are out-performing their share of registered voters in absentee ballot requests and early votes, the campaign said.
"The battleground state polls are all very close, although many are still tipping slightly Obama's way," Miringoff said. "It's still very much a flip of the coin situation."