Even the chairmanship, however, may not be the end of this ascent. For this is also an essay in another well-known American genre, the campaign biography. About a year before the presidential election, would-be candidates like to publish an authorised biography. This serves several purposes. It advertises the candidate's suitability without committing him to running. It puts the candidate's version of his career on the record. It provides journalists with instant material for profiles. And, incidentally, it raises some money at the very moment when a potential candidate needs it to get his campaign under way.
In Powell's case, the American publisher, Random House, is reported to have advanced $6 million against royalties, eclipsing even the $4 million Rupert Murdoch's Harper & Row offered to Speaker Newt Gingrich. (The Speaker, surprised by the storm of protest, accepted only a token dollar, confident that he will get the money anyway after publication.)
No fewer than 800,000 copies have been trucked into America's bookstores, and the General is involved in a blitzkrieg of talk-shows, book-signings, advertising and political pipe-sucking. No one seems in much doubt that Powell wants to be President. Nothing else, however, about his political intentions is clear. Is he, to begin with, a Democrat or a Republican?
He sounds like a Democrat. He is, for a start, an African-American, born a member of a group whose vast majority, mindful of the support they received from Franklin Roosevelt, John Kennedy and Lyndon Johnson, have been reliable Democrat voters. Roosevelt was a hero in his boyhood home, and he points out that he received a free education at City College because New York taxed its citizens to invest in the children of immigrants and the working class.
Yet now Powell has announced that he has no interest in the Democratic nomination. So is he a Republican? Well, he is a fiscal conservative. And he writes: "Everything I observe affirms my belief in free enterprise." He felt comfortable with high office under the Reagan and Bush administrations. He was President Bush's national security adviser, and his memoirs make plain his admiration for Reagan who, he thinks, restored to America a faith in the simple values he cares most about: religion, patriotism, thrift, family and duty.
If Powell is a conservative, though, it is of the old-fashioned kind, not of the abrasive, devil-take-the-hindmost school of Gingrich. As a black man who has made it to the apex of American society, Powell is full of gratitude as well as pride. But he cannot ignore the racism he has encountered. As a young officer at Fort Benning, Georgia, he was refused service at a drive-in hamburger joint. He makes it plain that he regarded the South's numerous military bases as "healthy cells in an otherwise sick body", not a popular view with today's Republicans. He is proud to have fought in Vietnam, but outspoken about the failures of American policy there. He is blunt about the shortcomings of American society, sympathetic to the unfortunate and sharply critical of the likes of Dan Quayle.
What Powell would like, it seems plain to me from his book, is to emerge as a third-party candidate like Ross Perot. But that will be a rocky road. The odds are stacked against any third-party candidate, especially - like Powell, but unlike Perot - one who will be dependent for resources on what he can raise.
Yet such is his combination of ability and experience, quietly held moral values and sheer personal charm that, especially in the present volatile climate of American politics, I do not believe that anyone can rule out his chances.
At least one of the heroes of every successful American war has gone on to the White House: George Washington, Andrew Jackson after the war of 1812, Zachary Taylor from the halls of Montezuma, Ulysses S Grant and Teddy Roosevelt from the Spanish-American war and Ike, supreme commander in the Second World War. Douglas MacArthur, who tried and failed to join that lineage, reminded us that old soldiers never die, they just fade away.
Even if Colin Powell does fade away, he has written a book of unusual interest. His account of growing up black in "Banana Kelly", the South Bronx neighbourhood where his parents lived before they won on the "numbers" lottery and moved to suburban Queen's, is as well done as his account of the Gulf War in which, he subtly suggests, Stormin' Norman Schwartzkopf did not display quite such confidence as it appeared.
Colin Powell is a soldier from his cap to his boots, but he has some engagingly human traits, and he doesn't mind owning up to some of the less disqualifying of them. He lost his pistol on one of his first assignments as a young lieutenant in Germany, and it didn't stop him coming back as commander of an army corps 30 years later. Shortly after retiring from the army, he ran out of gas on the Beltway, the orbital motorway which divides Washington from red-blooded America, and - we are left to infer - that won't necessarily mean that his career inside the Beltway is out of gas.
His hobby is fixing up ancient Volvos. "My idea of a good time is to disconnect every wire, tube, hose, cable and bolt of an engine ... as I stand there, grease-stained and triumphant". This may be a campaign biography, but the campaigner comes across as a nice man, with a sense of decency and a sense of humour.
It also leaves a thought for us to ponder. When his mother died, he found the British passports his parents had taken with them to New York, "two solemn-faced black immigrants from a tiny British colony" whose son was about to be knighted by the Queen of England. Had they, he reflects, shipped out for Southampton instead of New York, he might have made sergeant-major in a modest British regiment, but not British defence chief. I don't think we can argue with that, and the idea that we cannot plausibly claim that we offer a fair chance to people like Colin Powell does not fill me with pride.