By Steve Schifferes
John McCain has pulled out of Michigan as his support ebbed
After three weeks in which the US financial crisis has dominated the news, the political landscape of the election has been steadily changing.
There has been a consistent - and significant - shift in the national opinion polls against Republican candidate John McCain, who is now running about 5% behind Barack Obama.
Even more important for the electoral battle has been the shift in the swing states, which is changing the landscape of the election and providing both campaigns with new opportunities and new challenges.
KEY BATTLEGROUND STATES
New in 2008:
Colorado, Virgina, North Carolina, Indiana
Key swing states in past elections:
Michigan, Pennsylvania, Ohio, Florida
The decision of the McCain campaign last Thursday to withdraw from Michigan - once considered a key swing state - is just one sign that the two campaigns are reconsidering their strategy with just four weeks to go before the election.
Of course, just as it seems that the economic crisis has helped boost Mr Obama's standing, other events - such as a foreign policy crisis - could help Mr McCain.
But both camps need to take critical decisions on which states to concentrate on, where they believe the election will be decided - a decision that is particularly acute for the McCain campaign.
Mr McCain cancelled some campaign appearances and spent the weekend in his ranch in Arizona with his advisers discussing how to approach the final weeks of the battle.
Broadly, the new geography of key swing states has made the South and the West more important, at the expense of the traditional battleground of the industrial mid-West.
One sign of the changed landscape is in the fact that recent polls give Mr Obama a slight edge in both Virginia and North Carolina, two states rich in electoral votes which together would more than counterbalance Florida. Both states were won by George Bush with handsome majorities in 2000 and 2004.
It is no surprise that Mr Obama has visited North Carolina 30 times, including twice in the past week, and Virginia 22 times.
And polls in Florida, where McCain had been leading and which voted Republican in the last two elections, seem to have shifted significantly, returning the state to its traditional battleground status. Florida has many retirees whose savings might be affected by the financial slump, and has been severely affected by the sub-prime crisis.
Mr Obama has been campaigning hard in North Carolina
The other key battleground now seems to be the Rocky Mountain states of Colorado, New Mexico and Nevada.
Mr Obama seems to be building up an unstoppable lead in New Mexico, the US state with the highest proportion of Hispanic voters.
But Colorado and Nevada - both easily won by George Bush - now seem too close to call. In the past two weeks Senator Obama has held four rallies in Colorado: in Denver, Golden, Pueblo and Grand Junction.
The new geography also seems to be having its effect on some Senate races. The Democrats look set to pick up the open two Senate seats in New Mexico and Colorado previously held by Republicans.
They are also running neck-and-neck in North Carolina, where Senator Elizabeth Dole - the wife of former Republican presidential candidate Bob Dole - is being challenged by another woman, Democrat Kay Hagen.
Even in Mississippi, which has been solidly Republican, the Democrats appear to have a chance to win the Senate seat that was vacated by Republican Senate leader Trent Lott when he stepped down.
Some estimates suggest that, if the Democrats pick up other marginal seats in Alaska and Oregon, they may increase their numbers in the Senate from 51 to 58 seats.
Defending his turf
Meanwhile, Senator McCain is being forced to defend some states that were considered safe territory just a short while ago - especially in the "rust belt" in the North-east and Mid-west.
Economic decline has hit Michigan hard
Recent polls have put both Indiana and West Virginia - which were considered strongly Republican - into the "toss-up" category - as well as Missouri, a bellwether state in national elections, where Mr McCain campaigned over the weekend.
"That is a lot of defence that John McCain is going to have to play," said David Plouffe, Mr Obama's campaign manager.
Meanwhile Senator Obama seems to be lengthening his lead in Iowa, won by the Republicans last time, as well as in Wisconsin and Pennsylvania, while Ohio may still be close.
However, even in Ohio, where the latest opinion poll gave Mr Obama a 49% to 42% lead, the Democrats were sounding optimistic.
"Very confident, yet not overly so," said Ohio Democratic Party chief Chris Redfern, who added that the financial turmoil is dreadful for the country but "politically it's advantageous" for Senator Obama.
The political director of the McCain campaign, Mike DuHaime, accepted that the landscape was shifting.
"This overall environment we face is probably the worst environment for a Republican in 35 years, and anytime you have that, you have states that will move," he said after announcing his campaign's withdrawal from Michigan.
Electoral college balance
The changing landscape has produced a big change in the hypothetical balance in the electoral college if the presidential election were held today.
Several election websites predict that Senator Obama is now ahead in in enough states to have between 250 and 260 electoral votes - close to the 270 needed for victory. Senator McCain is projected to have secured less than 200 electoral votes, while the remainder are still up for grabs.
Of course, these are only projections based on opinion polls. Some voters could still change their minds, and others may not turn up at the polls.
So both campaigns will redouble their efforts to get out their own supporters, as well as trying to appeal to the shrinking number of independent or undecided voters.
But with voting already beginning in some key states like Ohio, it is the McCain campaign that will have to seize the initiative if it is to turn around the race.