Editor's Note: Due to the electoral college system in the US, presidential elections are determined by results at the state level, not the total national vote.
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By John Whitesides, Reuters Political Correspondent
With one month left in the campaign, Republican John McCain's path to the White House has become perilously narrow as Democratic rival Barack Obama gains momentum in crucial battleground states.
Sen McCain is fighting to hold several states won by President George W Bush in 2004, including highly contested Florida and Ohio, and is playing defense against a surging Sen Obama in traditionally Republican states like Indiana and North Carolina.
The deepening economic crisis and prolonged negotiations on a $700 billion bailout of US financial institutions have played to Sen Obama's perceived strengths on the economy, helping the Illinois senator gain a solid lead in national opinion polls and pick up steam over the last few weeks.
'McCain has no more margin of error - he must sweep most of the key battleground states,' said Peter Brown, assistant director of the Quinnipiac University poll. 'He needs to draw an inside straight to win.'
Recent polls show Sen McCain in a dogfight in Ohio, Florida, Virginia, North Carolina, Colorado, Missouri and Indiana. All were won by Bush in 2004 and Sen McCain cannot afford to lose them as he tries to piece together the 270 electoral votes needed to capture the White House.
'If McCain loses even one of those he's toast,' Mr Brown said.
The pressure on Sen McCain was highlighted by his decision on Thursday to pull staff and advertising from Michigan, won by Democrat John Kerry in 2004, for the end drive to the 4 November election.
Sen Obama has a double-digit lead in two recent polls in that state, home to the automotive industry and a distressed manufacturing-based economy.
'If we see a swing back in our favor, we'll go reengage,' McCain adviser Greg Strimple said.
Sen McCain advisers said they would launch an aggressive advertising campaign against Sen Obama in traditionally Republican states like Indiana, which has not voted for a Democrat for president since 1964, and said that should snap them back into a lead.
'Get to know Obama'
'We're going to make sure everyone knows who Barack Obama is,' Mr Strimple said. 'And once they do, we believe the state will come back reliably Republican as it's always been.'
Sen Obama appears to be in a strengthening position to hold all or nearly all of the states won by Kerry in 2004, including one-time toss-up New Hampshire and its four electoral votes where recent polls give him a double-digit lead.
He also looks to be on track to recapture Iowa and New Mexico - two states won by Bush - for Democrats, putting him just six electoral votes shy of the 270 he needs to win.
Under that scenario, breakthrough victories in any of several remaining battlegrounds like Virginia, Colorado, Ohio and Florida would put Sen Obama in the White House.
'We have been playing a lot more offense than McCain has,' Obama campaign manager David Plouffe told reporters. 'To be as strong as we are in Virginia, Colorado, Iowa, New Mexico, Florida, Ohio - a lot of our key take-away states - we feel very positively about where we are.'
Mr Plouffe said the campaign was particularly encouraged about Florida, which decided the 2000 election. Sen McCain has virtually no chance to win without Florida, and four new polls this week gave Sen Obama a lead of three to eight percentage points.
'Florida is a big deal,' Plouffe said. 'A state with 27 electoral votes, that they thought was going to be in their base column, could not be more competitive.'
Republicans hope the pendulum began to swing back their way on Thursday with a steady performance by Sen McCain's running mate, Alaska Gov. Sarah Palin, in a debate with Democratic vice presidential hopeful Joe Biden. Sen McCain and Sen Obama have two more debates, with the next on Tuesday in Nashville, Tennessee.
Sen McCain hopes to shift the focus of the race away from the economy and back to questions about Sen Obama's experience and voting record.
'We're looking to turning the page on this financial crisis and getting back to discussing Mr Obama's aggressively liberal record and how he will be too risky for the Americans,' Mr Strimple said.
Whether Sen Obama's recent gains are the peak in a typical campaign cycle of peaks and valleys or the start of a more significant movement toward a big Democratic victory could become clear over the next two weeks.
'If the election were today Obama would win by a comfortable margin,' Brown said. 'But it's possible we're at a tipping point for Obama where he wins in a Democratic landslide we haven't seen since 1964.'
