If Barack Obama is elected president of the Uni ted States, it will be the result of another presidential election back in February 1990. At that time, 80 of his Harvard classmates chose him to be the first black scholar to edit their law review. That instantly brought him to national attention, with articles in the New York Times and other major papers, a book contract and 700 job offers from all the best law firms. He was a mat ure student of 28 at the time and, after graduation, worked for several years as a community lawyer before ascending the greasy pole of Illinois politics. What does this period of his life foretell?

There are very few back issues of the Harvard Law Review available in the UK. I tracked down volume 140 on a deserted floor of the Middle Temple library, above the amazing Molyneux globe that guided Sir Walter Raleigh to the New World. It was unthumbed and weighed in at 1,964 pages, comprising learned articles, students' case notes and book reviews, with many thousands of footnotes. The university law review is an American phenomenon that has no parallel in our lazier and less academic law schools: the notion of an elite group of students determining the focus of contemporary legal thinking would cause apoplexy in Oxbridge common rooms. But in the US, law reviews are important in shaping the law, and Harvard's is the most important of all.

Hence the newsworthiness of Obama's election. Never before had there been a black editor-in-chief. "The fact that I've been elected shows a lot of progress," he said at a press conference. "But you have to remember that for every one of me, there are hundreds of thousands of black students with at least equal talent who don't get a chance," he said, alluding to poverty or growing up in a drug environment. It was a worthy beginning, and earned him an affectionate imper sonation in that year's Harvard Law Revue ("In Chicago I discovered I was black, and I have remained so ever since").

The 1990-91 legal term was an unsettling and unsettled time. Justice William Brennan, architect of Supreme Court activism (such as the New York Times v Sullivan case, a foundation of US press freedom), had just retired, and Obama's volume begins with a tribute to him from Thurgood Marshall, the court's first black justice. William Rehnquist now held the reins, and Ronald Reagan and George Bush appointees were in the majority: the candle of liberal juris prudence, burn ing bright in classrooms inspired by the phil osophy of Ronald Dworkin, was beginning to gutter.

Volume 140 is full of civil liberties issues (Obama had been an editor of the previous year's Civil Liberties Review) and full of apprehension lest Dworkin's moral theories should cut no ice with the conservatives on the Supreme Court. The first major article (solicited, it was noted with surprise, from a non-Ivy League professor) analysed the philosophy of Václav Havel, and argued that his "individual responsibility" approach might be better suited to protecting free dom than Dworkin's appeals to individual rights. Volume 140 exhibits a refreshing interest in foreign cases (some Republican justices regard the citation of UK court decisions as tantamount to treason), and there is a contrast between the views of Stephen Sedley QC on the need to censor hate speech and the American Civil Liberties Union's support for the right of racist utterance.

Rhetorical genius

Barack Obama leaves no byline in this volume, but as president he was responsible for selecting the topic of the major student disquisition: a 180-page analysis of the need for new laws to protect the environment. Introduced with quotations from Chekhov, U Thant and the Grateful Dead, it appears prescient today: it was produced long before climate change became topical and its advocacy of "green helmets" and extraterritorial law enforcement against corporate polluters is more relevant than ever.

It is tempting to detect the young Obama's hand in a few of the many unsigned articles and book reviews. There is a scathing dismissal of a book by Roy Grutman, a great courtroom advocate ("Money is what makes his legal world go round"), reminiscent of Obama's later comments that the law "is a sort of glorified accounting that seems to regulate the affairs of those who have power". And I strongly suspect his contribution to the last and best article in volume 104, entitled "Talking of unconscionable niggers".

This is an acidic review of a biography of Frederick Douglass, the slave who became a formid able orator for abolition and later a respected public servant (the title is a quoted reaction to Douglass's modest request to be paid for his services). The review notes how most white abolitionists (including Abraham Lincoln) were opposed to equal rights for freed slaves, and severely criticises the author (a white historian) for failing to notice black women. This is not an admission that Obama - who was shortly to marry Michelle (she had graduated from Harvard before him) - could readily forgive.

Obama himself graduated with the legal world at his feet. He could have taken a highly paid job at a prestigious law firm, or a year's clerkship with a Supreme Court justice, followed by an even higher-paid job. Instead, he returned to community work for a small firm in Chicago that specialised in housing, welfare and employment and that paid him a modest $167 an hour. For all his rhetorical genius, he never tried a case, preferring the solicitor's work of researching briefs and preparing witness statements. His clients were whistleblowers and non-governmental organisations anxious to use the law to assist the registration of voters who were poor and black and mainly Democrat. In 1996, Obama was elected to the Illinois state senate, although he continued to lecture for 12 years on constitutional law as a visiting professor in Chicago. By all accounts, especially those of his students, he was an outstanding teacher.

There is one abiding mystery about Obama's legal career. Although (as his books attest) he is a fine writer, he never put his name to any article, anywhere. But it was a time when the very ambitious had become very cautious: Robert Bork had been denied Supreme Court confirmation on the strength (in fact, the weakness) of his earlier writings, and the mysterious David Souter passed muster only because he had written nothing that Democrats on the Senate's judiciary committee could sink their teeth into (to Republican fury, he turned out to be a closet liberal). Perhaps young Barack decided to leave no hostages to fortune in a career trajectory that could take him to the Supreme Court - or to the White House. Or perhaps he was too busy with his humble work in and for poor commu nities to bother about reshaping a legal system that he had come to believe would inevitably serve the powerful.

Ironically, it is that system which is most at stake in this election. George W Bush leaves a bloc of four dyed-in-the-wool conservatives seated for many years to come on the Supreme Court of nine judges. Three of the remaining moderates (Justices Stevens, Ginsburg and Souter) are likely to leave in the next few years. "Gentleman John" McCain has promised to appoint strict constructionists, judges who will find no constitutional bar to executing juveniles, or limiting abortions or abolishing habeas corpus. The fate of liberal jurisprudence hangs once again in the balance - as it did, in 1990, for the president of the Harvard Law Review.

Barack Obama's legal career never took off, for all its historic promise at Harvard. He turned his back on the glamour of trial attorneyship and the megabucks of a prestige partnership, preferring to help house the poor. That may have been the result of careful calculation, as the quickest way to a political career. Or it may simply be that Barack Obama, despite being a lawyer, is a really good person.

Geoffrey Robertson QC is the author of "The Justice Game" (Vintage) and a member of the UN's Internal Justice Council