Barack Obama is drawing up plans for an audacious final push deep into the Republican heartland to force John McCain to spend valuable time and money defending states that were not considered potentially vulnerable even a few weeks ago.

After Mr McCain failed to change the dynamic of the race during the final presidential debate on Wednesday night, he faces an electoral map today with a harsh reality: he must now win virtually all of the eight “toss-up states” on election night to eke out victory. Mr Obama, riding a surge of momentum courtesy of voter concern over the economy, needs to win only one to enter the White House.

With the race now tilted significantly in Mr Obama’s favour, the mood of voters is so volatile amid the economic turmoil that polls have even begun to narrow in such reliably Republican states as Arkansas and Kentucky. The Democratic candidate is due to run advertising in West Virginia, which President Bush won by 13 points in 2004 but where the ground has shifted towards him in recent days.

Democratic strategists said that Mr Obama was also considering pouring money back into North Dakota and Georgia, two heavily Republican states that he abandoned this year when they appeared out of reach.

Mr Obama cautioned his supporters yesterday against preelection hubris, invoking his surprise loss in the New Hampshire primary against Hillary Clinton in January that threatened to derail his campaign after his opening victory in the Iowa caucuses a few days earlier. “For those of you who are feeling giddy or cocky or think this is all set, I just have two words for you: New Hampshire,” Mr Obama told donors at a Manhattan fundraising breakfast. “I’ve been in these positions before when we were favoured, and the press starts getting carried away and we end up getting spanked.”

Most pollsters predict that the race will tighten as election day draws nearer. Karl Rove, Mr Bush’s former chief strategist, wrote yesterday that “the outcome of the race isn’t cast in stone yet”, mainly because nearly half of voters still do not believe that Mr Obama is qualified to be president.

Yet Mr Rove also conceded that with only 18 days left, Mr McCain is running out of time, and that if he does win, he will “have engineered the most impressive and improbable political comeback since Harry Truman in 1948”.

Mr Obama now enjoys a lead in national polls of between eight and ten points. But it is the state-by-state electoral map that makes clear the scale of the challenge now confronting Mr McCain. To win on November 4, a candidate needs 270 electoral college votes. If all the states that are likely wins for each candidate, or leaning towards them, are added together, Mr Obama has 264 electoral college votes to Mr McCain’s 163. That leaves the eight toss-up states – Nevada, Colorado, Missouri, Ohio, Florida, Indiana, Virginia and North Carolina – with a combined total of 111 electoral college votes, to decide the race.

All are states won twice by Mr Bush. Virginia has not backed a Democratic presidential candidate since Lyndon Johnson in 1964, yet Mr Obama has pulled into a lead of between five and ten points. Three months ago the critical battleground of Florida looked unlikely for Mr Obama. Today he has a five-point lead. Mr Bush won Indiana by 21 points in 2004. Today Mr McCain is holding on to a tiny lead. In Colorado, Mr Obama is about five points ahead.

If Mr McCain loses any of them, or indeed the hugely important battleground of Ohio, where he is slightly trailing, his presidential hopes will be over. He is more aware than anybody that no Republican has ever won the White House without Ohio.

Democrats, scarred by the 2000 Florida recount and John Kerry’s loss four years ago, are so haunted by those defeats that many still fear some stunning external event, or revelation about Mr Obama, will emerge to rob them of victory once again. Yet with 18 days left, some are now daring to believe that Mr Obama will not only prevail on November 4, but could even be heading for a landslide victory.

Last night the Republican National Committee released its latest advertisement focusing on Mr Obama’s lack of experience and lingering concerns that he is not ready to be president.

With a camera aimed at an empty Oval Office chair, it says the country is considering elevating “one of the least experienced people ever to run for president”, adding: “This crisis would be Obama’s first crisis – in this chair.”

The Virginia Republican party released a mailshot featuring a close-up of an unknown dark-skinned man and the words: “America must look evil in the eye and never flinch.” A party spokesman could not say whether the photo depicted Mr Obama.

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