Watergate hardly gets a mention in this film. We see the 'plumbers' donning rubber gloves, and the president fumbling with a few of his tapes, but detail is almost totally eschewed. There is no Egil Krogh, no Jeb Magruder. Kleindienst and Gray are mentioned only in passing. Cox is fired by way of a spoken TV bulletin, Jaworski is not referred to at all. We do not see anything of the titanic courtroom struggles, with all three branches of the federal government locking horns. Though we are told that the American Constitution is self-righting, like a boat immune from capsize, we are not shown how or why.

And in this, Oliver Stone is perfectly right. As it stands, the film is very long, and dense with detail. There is no room for the minutiae of the cover-up, which in any event would make for a confusing narrative. Stone's subject is Nixon the man, not the edifice that toppled around him.

And what a man. Richard Milhous Nixon is a truly fascinating personality - both statesman and charlatan: ruthless and vulnerable: unable to express his emotions, yet the most emotional of politicians: a man who spent his life in the law and in high office, but who never absorbed the legal and ethical mores of public life. Genius and crook, bold visionary and spiteful backstabber, Nixon will continue to spellbind biographers for decades to come.

"That's when it starts," says Stone's Nixon, "when you're a kid." The film takes us to Whittier, California in 1925 to see the unloved boy who struggled painfully to earn his parents' approval, without ever quite succeeding. As a teenager, he levered his way into the school football squad by sheer willpower. Lacking talent, he doggedly subjected himself to repeated physical battering in the scrimmages, "a tackle dummy with guts". This syndrome recurs throughout his career. Always susceptible to scathing criticism, never quite commanding respect, Nixon never the less kept ploughing back into the melee when wiser, lesser men would have quit. It is hardly surprising that the years of punishment should have left psychological scars.

Nixon's hatred of John Kennedy had more than one source. He was devastated by the defeat in the 1960 presidential election, but not simply because of disappointment at losing, or even because the Kennedy victory carried the odour of fraud: bitterest of all for Nixon was the realisation that the Kennedy people had played hardball more effectively than the Republicans. Nixon had been out-sharked, and it hurt. On a more profound level still, John Kennedy was everything that Nixon could never be. He was a smooth, handsome prince among men, exuding poise and confidence, a patrician imbued with the habit of authority. To Nixon, the perpetual outsider, the quaker geek who looked shoddy and disreputable, Kennedy seemed to have the dice unfairly loaded in his favour. JFK was an East Coast bright boy and war hero, fabulously wealthy and impeccably well-connected. Nixon owned nothing and knew nobody, and was all too obviously 'on the make'. The great witch-hunts, of Hiss in the 1940's and Ellsberg in the 1970's, are manifestations of the chip on Nixon's shoulder, the fathomless bile that he directed at East Coast college boys.

Nixon always imagined that he was hiding his pain from the world, whereas in fact it was on global display. His nervous little laugh at moments of emotional crisis was so false, so gut-wrenchingly inappropriate, that the onlooker could catch a glimpse of the man's tortured soul. Hopkins captures the wretched laugh with devastating effectiveness, both in the scene where Nixon is confronted by a hostile man in the TV studio audience, and when he solemnly promises that none of the president's men will go to jail. In the "Checkers" broadcast and the presidential TV address on Watergate, Nixon tries to assure the camera that he is not a crook, and on both occasions he has the exact opposite effect, confirming to the viewer that that is precisely what he is. Nixon seems incapable of examining his own conscience: there is a hard core which his rational mind cannot penetrate. Maybe that is why Stone has him referring to himself in the third person throughout the film.

'They' were always out to get Nixon, without it ever being made clear just exactly who 'they' might be. The imperative for this deeply paranoid man was always to be braced, ready for the coming tackle, or to organise pre-emptive strikes against 'them'. Obstructing justice and tampering with evidence were, to Nixon, self-defensive steps that did not need to be justified. It was obvious that such things had to be done. The mystery at the heart of Watergate - why a president so steeped in criminal conspiracy should tape-record his own intimate conversations - makes sense when viewed from Nixon's end of the telescope. He had to have the goods on his own men, ready for the day when they turned on him. It goes even further. This emotional cripple could not bare his bleeding soul to anyone, so his tapes became his confessional and his confidante. Stone's film repeatedly shows Nixon in his awkward arms-extended, double V-sign pose. It is not by chance that it looks like a crucifixion.