You know what they say: the only poll which matters is the one on election day.

During the 1980 campaign I was at lunch in the cavernous ballroom of the then largest hotel in Washington, the Sheraton. The speaker was Joseph McCaffrey, the influential Capitol Hill radio commentator whose broadcasts were heard nightly across the nation. “Come November,” he told his audience of some 700, “and Reagan will ride off into the sunset without his girl. He'll be lucky to have his horse.” As you will recall, he did ride off — into the White House for eight years.

I can even remember the front page of the New York Times on November 5, 1948. ‘Dewey Defeats Truman,’ it roared in characters two inches high. It was a headline based on the polls. They were unanimous that Thomas Dewey, the Republican Governor of New York and a rich New York lawyer, was on his way to the White House. But he was not. Harry S (for nothing in particular) Truman in many ways was an unlikely victor. He had only inherited the presidency — when the great Franklin Roosevelt died in office in 1945. But no one thought that later he would actually be elected to it.

The main reason was his ordinary personality. He had been a farmer in Independence, Missouri who later became a draper in that unknown small town. But when FDR died, Vice-President Truman was thrown in at the deep end. He went to the Potsdam Conference outside Berlin when scarcely three months in office and sat down with old hawks like Stalin and Churchill to plan the post-war world. Weeks afterwards, having planted a small plaque on his desk declaring that, “The buck stops here”, he sent the Super-Fortress, Enola Gay, to drop an atomic bomb on Hiroshima; and when the Japanese still refused to surrender, had another dropped on Nagasaki. Later, by launching the Marshall Plan of aid to Europe, he laid the foundations of both Nato and the EU and, by enunciating the Truman Doctrine, promised that the US would support free nations suffering subversion or aggression.

Perhaps his greatest and most attractive trait was that he was patently unspoiled by success. The day he left office, his former Secretary of State, Dean Acheson, gave a small lunch for the retiring President at his Washington home in Georgetown. When Truman emerged afterwards to drive away, he found a hundred people waiting outside in that quiet and elegant residential suburb to see him off. He made a short speech — just two sentences. “Your coming today,” he said, “means more to me than many grander, formal occasions. Now I'm Mr Truman, private citizen.”

And so he went home: to Independence, to the very ordinary two-storey house, the only one he ever owned. “I took the case upstairs, just like old times,” he said.

It could not happen today, even were the outgoing president more popular than George Bush. The media would have blocked the street in Georgetown, for one thing. That being so, I believe we have lost something; for the change in the political landscape has also changed the candidates. A man like Truman would stand little chance in the presidential stakes today. He would be reckoned quite colourless — and too poor. Today, the candidates are packaged, gilded — and sold in operations costing billions of dollars. Accordingly, if we are wise, we judge them with a healthy scepticism. In Truman's case, what you saw was what you got. It is not the case now. What we read and see are largely the filtered words and pictures the spin doctors intend us to see.

Seldom if ever has the coverage of an election campaign been the occasion of such one-sided partisanship in the English-speaking mass media as the American one which climaxes today. The media virtually are of one mind: Obama must win. They may be right. But open partisanship of this kind is an extra hazard for those seeking the truth. Who is Barack Obama? After the copious acres of coverage, and the mass-migration of reporters across the Atlantic, few of their readers or viewers on this side would admit that they know.

He was brought up, first in Kenya, the son of an alcoholic womaniser of a father and, as a child, lived for four years in Indonesia with his mother and her second husband. She subsequently put him in the care of grandparents who paid the fees to send him to the most exclusive private school in Hawaii. But the most significant fact about the adult Obama is that he cut his political teeth in Chicago. He would be the first president in living memory to come out of the devious rough-house of midwestern machine politics. I know the old city well. Accordingly, if he wins, I would warn to prepare for surprises.