Washington - Economic fears among voters have produced a seismic shift in the U.S. presidential election in key swing states.

    According to a spate of new polls, contests that for weeks seemed to be toss-ups, such as Pennsylvania, Michigan and Iowa, have swung solidly in favour of Democratic presidential nominee Barack Obama. And several states that appeared to be safely in hand for Republican John McCain, including Ohio, North Carolina, Missouri and Nevada, have become the new battlegrounds.

    At the state level, the situation for Mr. McCain is becoming desperate.

    A week ago, all eyes were on Pennsylvania. The Republicans were challenging the Democrats in this key battleground state, with two different polls showing both candidates in a dead heat.

    Not any more. A Quinnipiac University poll released yesterday puts Mr. Obama ahead of Mr. McCain in Pennsylvania by a whopping 15 points, 54 per cent to 39 per cent.

    Three other recent polls, by Fox News/Rasmussen, Franklin and Marshall and Morning Call, all put Mr. Obama ahead by seven or eight points.

    In Michigan, the other battleground state that the Democrats took in 2004 and simply must hold if they are to win in 2008, a recent Detroit Free Press poll had Mr. Obama in front by 13 percentage points.

    With Mr. Obama comfortably ahead in the big states where he was considered most vulnerable, attention is shifting to two key states that the Republicans took last time out: Ohio and Florida.

    Quinnipiac has Mr. Obama eight points up in Florida, while a CNN/Time Magazine/Opinion Research poll also released yesterday has Mr. Obama ahead 51 per cent to 47 per cent. A recent survey from Public Policy Polling has Mr. Obama up three points, while Fox News/Rasmussen has the race tied.

    This is a marked change from previous data, which showed Mr. McCain with a modest but consistent lead in the Sunshine State.

    Quinnipiac also has Mr. Obama up eight points in Ohio, although other surveys show the race essentially tied. Again, most previous polls showed Mr. McCain modestly ahead in the state that tipped the election for President George W. Bush in 2004.

    There are two possible explanations for this shift. The first is that the polls are wrong.

    On the website Politico.com, an unnamed McCain source described the entire Quinnipiac survey as "laughable."

    "Our polling shows us up seven" in Florida, the source said. "My guess is they oversampled blacks and undersampled Cubans."

    But although the Quinnipiac gaps are more emphatic, most polls have registered a shift in Mr. Obama's favour at the battleground-state level over the past week.

    Which makes the second possible explanation more credible.

    "There are three things driving this election right now: the economy, the economy and the economy," said Clay Richards, assistant director of the Quinnipiac University Polling Institute, in an interview.

    Voters have long rated it the most important issue, and they have long trusted Mr. Obama over Mr. McCain to manage it. But that trend is accelerating.

    In Florida, for example, the Quinnipiac poll shows 60 per cent of voters now rate the economy issue No. 1. And 53 per cent of all voters said they preferred Mr. Obama on the economy, compared with 39 per cent for Mr. McCain.

    Unless the current economic crisis recedes in importance over the remaining 33 days of the campaign, or unless Mr. McCain can reverse the majority perception that the Democrats are a better bet on economic issues, then the Republicans are headed for a difficult day Nov. 4.

    The trend line in other battleground states is also swinging pro-Obama. The last five polls in Colorado, formerly a safe Republican state, all put Mr. Obama in the lead, with a range of between one and nine percentage points.

    Four of the last six polls in Virginia show Mr. Obama in the lead, although narrowly. Time/CNN, however, has Mr. Obama up nine points in Virginia.

    North Carolina is in play, with two of three recent polls showing the Democrats slightly ahead. And Iowa, which went Republican in 2004, is now considered certain to go Democrat in November.

    Tiny New Hampshire is the only state that went Democratic in 2004 that the Republicans have a reasonable chance of winning this year.

    This means that there is only one path to victory for Mr. McCain: hold on to every state that George W. Bush won in 2004. Mr. Obama, however, has many paths. If he grabs either Ohio or Florida away from the Republicans, then the election is his.

    Even if the Republicans hang on in these battlegrounds, Mr. Obama could prevail by assembling a consortium of two or three formerly Republican states where he is currently ahead or running close behind. These include, as well as the states described above: Missouri (where Time/CNN has Mr. Obama moving into a one-point lead; Nevada (where the same poll has Mr. Obama up by four points), Indiana, and New Mexico.

    These new state polls come at a time when both Gallup and Washington Post/ABC News actually show the race tightening nationally. The latter had Mr. Obama's lead nationally at nine points last week; this week it's at four. Gallup's daily tracking survey shows Mr. Obama's eight-point gap of three days ago down to four points yesterday.

    But Pew Research, Time/CNN and Associated Press/GfK all released polls yesterday showing Mr. Obama seven points ahead of Mr. McCain.

    The Time/CNN poll has Mr. Obama at 50 per cent and Mr. McCain at 43 per cent. "No Democrat has crossed the 50 per cent threshold in the general election since before Ronald Reagan was elected," Time reported on its website.

    So is this race over? Heck, no. If Republican vice-presidential candidate Sarah Palin exceeds expectations tonight or if Mr. Obama performs poorly in the two remaining presidential debates, the narrative could shift. And as Mr. Richards observes: "The one thing you can predict in this campaign is that it's unpredictable."

    Mr. McCain could use a very strong dose of unpredictable, right now.