PITY the American voter in Ohio and the dozen other battleground states, especially if they are undecided. They are about to be bombarded by the most sophisticated and relentless canvassing operation that democracy has yet devised.

Pity, also, the overwhelming majority of Americans who live in the three dozen other states where the result of the presidential election in November is considered a foregone conclusion. Their votes are virtually worthless.

More than ever before, the presidential election this year will be focused on the shrinking number of swing states that determine the result. And in a nation split 50/50 even before President Bush further polarised the camps, the number of swing voters will also be close to a record low.

In 2000, fewer than 10 per cent of Democrats voted for Mr Bush, and a similarly small percentage of Republicans backed Al Gore, the lowest crossover vote ever recorded. Analysts expect those figures to fall further in November.

Thomas Schaller, a political science professor at the University of Maryland, said that up to 160 million voters will be discounted by either side because they live in either confirmed “red” Republican states or habitual “blue” Democrat ones.

“The election is going to be extraordinarily close, unless the economy has a real crash or a real rebound,” he said, “but there are a decreasing number of states that are in play; 80 per cent of the population are on the sidelines.”

Other strategists believe that once the parties discount voters who have already made up their mind, barely 10 per cent of the electorate are up for grabs.

The 2000 result shows how narrow the 2004 playing field is. Twelve states were decided by less than 5 per cent. In a handful of others, only demographic changes or sheer optimism make them competitive.

The Bush campaign launched its opening $4.5 million (£2.5 million) advertising campaign in 17 states. John Kerry’s Democratic team has its eyes on the same group.

They divide into five areas. The prime battleground is the Rust Belt of Ohio, Pennsylvania and West Virginia, all of which have suffered severe job losses in their steel and other manufacturing industries.

The states that straddle the Mississippi, including Minnesota, Wisconsin, Iowa and Missouri, will see fevered campaign action. Hopeful Democrats insist that they can prosper farther downstream in Tennessee, Arkansas and Louisiana. Democrats won Tennessee and Arkansas, home states to Mr Gore and Bill Clinton, twice in the 1990s, but that was against the trend of Southern states going Republican. Mr Gore failed to hold Tennessee in 2000.

Three southwestern states — New Mexico, Arizona and Nevada — will feature more prominently than in 2000, when Mr Gore won New Mexico by a smaller margin than he lost in Florida. An influx of Hispanics and white Californians fleeing fiscal mayhem in California mean that Republicans can no longer count on the other two.

Washington State and Oregon in the Pacific North-West both went narrowly for Mr Gore in 2000. On the East Coast, New Hampshire, the only New England state to back Mr Bush in 2000, is a key Democratic target.

Florida, because of its symbolism, has been subjected to a rolling low-level campaign for three years. Mr Bush has lavished the state with attention — and having a brother in the governor’s mansion helps.

Times Recommends

• Would you live on the wrong side of the Berlin Wall?
• Wish you were here, says Iraq tourist board
• Russian policeman’s corruption plea to Putin