Countless millions of words have been written, orated, argued over and forgotten in the course of the US presidential election but now, through some peculiar process of political alchemy, the battle has boiled down to two quintessentially American words: “cool” and “maverick”.

Barack Obama is cool. The overwhelming majority of people under the age of 30 identify this as the term that best describes the Democratic candidate. Put the words Obama and cool into Google, and it will spit out an astonishing 21 million hits. He is black, he is hip, he listens to Jay-Z on his iPod (and Yo-Yo Ma). He plays basketball. He fist-bumps. He is cool, a word that transcends age, race and gender.

John McCain is a maverick, both noun and adjective. The word has become his slogan. At a rally in Ohio this week, the Republican candidate appeared on stage for 11 minutes, and used the word four times. Sarah Palin has also adopted it, describing herself as “Mom, maverick and moose-hunter”. At the Republican convention, Mr McCain declared: “You all know, I've been called a maverick.” The word was printed on placards and deployed by speaker after speaker as a mantra.

This election is unique in the extent to which each candidate has become associated with a single word. Even more extraordinary is the way these terms represent both the best and the worst in the two men who would be president. Both words are double-edged: Mr Obama's coolness appeals to younger voters, but it could also lose him the election. Mr McCain's capacity for maverick behaviour scares as many people as it attracts.

Mr Obama would not be the first cool president. JFK was cool; so was Bill Clinton and so, in a strange way, was Ronald Reagan. (No senior British politician has ever been cool.) In American politics, the word was first used by Abraham Lincoln: “That is cool,” he said in 1860, when secessionists threatened to break up the union and blame it on him. “A highwayman holds a pistol to my ear and mutters through his teeth, ‘Stand and deliver, or I shall kill you, and then you will be a murderer!'.”

The word was rendered truly cool by black jazz musicians in the 1940s, and brought into the mainstream by Charlie Parker's 1947 Cool Blues and Miles Davis's 1949 album, Birth of the Cool. It has since been adopted by beatniks, hippies, advertisers, internet techies and everyone else. Slang terms of approbation tend to live fast and die young, but cool has survived like no other. It has even outlived the taint of being sucked into Blairite branding, in the “Cool Britannia” campaign.

As he responded to the failing American economy and the failed Wall Street bailout this week, Mr Obama was the epitome of cool: loose-limbed, joking and apparently unruffled. But he was also the less attractive side of cool, which verges on cold. Mr Obama's composure has enabled him to negotiate the white heat of American racial politics without breaking a sweat, yet that brings with it an aura of detachment. Describing the need for a deal to save the economy, he seemed almost aloof from the ferment.

Mr Obama's cool is central to his charisma, but even his strongest supporters fear he can seem distant, disengaged, even chilly. “Maybe he's just too cool to ever get hot, but the result is that we have little insight into his passions: what, above all, does he care about?”, wondered Washington Post columnist Richard Cohen.

No one ever uses the word cool of John McCain, except to wonder when the irascible war veteran will lose his. Mr McCain first adopted the maverick label in 2000, to hone his image as a contrarian, a rugged individualist, a man unfettered by party rules who knows his own mind and is not afraid to use it.

The original Samuel Maverick was a landowner and rancher in late 19th-century Texas, who never bothered to brand his cattle. Unidentifiable, wandering cattle became known as mavericks, and the word, infused with western individualism, gradually expanded to incorporate anyone refusing to toe the line. Sam Maverick was a great character, and a fine if inadvertent word-maker - he coined the term “gobbledegook” to describe the nonsense spouted by politicians; he was also a fantastic pain in the neck, causing neighbours endless trouble and expense by his selfishness.

Both aspects of being a maverick have been amply displayed by Mr McCain in the past two weeks: the decision to suspend his campaign and return to Washington was touted as an act of maverick inspiration, but in the end it did little to help the process, and may have hindered it by further inflaming congressional Republicans with little love for the Republican senator. Mr McCain ended up looking impetuous, almost deliberately obtuse.

He prides himself on marching to the beat of his own drum, but too much solo drumming can lead to deafness. A cussed belief in one's own opinions, a willingness to go it alone, a certain swaggering disregard for the views of others - these are all admired American qualities, but they also describe the maverick currently occupying the White House, whom most Americans cannot wait to see gone.

Cool Obama has recruited countless African-Americans and younger voters to his cause. Maverick McCain revived his flagging campaign by dissociating himself from an unpopular Republican Party and by showing a willingness to take risks, most notably by appointing Sarah Palin, the female incarnation of Sam Maverick, as his running-mate.

But as America's financial crisis deepens and the race heads into its last few weeks, both candidates are in the odd position of needing to distance themselves from the very words that made them: Mr Obama's hopes depend on being a little less cool, while Mr McCain should reassure his own herd by playing down the maverick brand.

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