But the constitutional separation of powers American-style can play some cruel tricks. While the head of the executive branch is parading around Manhattan as international statesman and self-appointed leader of the free world, the legislative branch - and much of the world's television audience - will be contemplating another President altogether. When Bill Clinton rises to address the UN, members of Congress will be 90 minutes into the four-hour videotape of his grand jury testimony about his "not appropriate" relationship with Monica Lewinsky, and the world's viewing public will not be far behind.
It is tempting to imagine the crossed cables and scrambled satellites that would have Mr Clinton reading the script of his testimony to an audience of shocked diplomats in New York, while a bored Congress fidgeted through a videotaped speech on terrorism... But the reality of the two shows playing concurrently worldwide will be bizarre enough.
While the best of Bill Clinton will be on display in New York - his natural authority, his innate sense of the dignity of his office, his measured embrace of America's global responsibilities, his easy personal charm and his facility in the realm of ideas - laid bare in Washington will be the very worst of Bill Clinton. And according to those few so far privy to the tape of the President's testimony from the White House Map Room, the worst is very bad indeed.
It was clear from his lawyer, David Kendall, immediately after the President had completed his fractured hours of testimony on that fateful Monday, 17 August, that his closed-circuit television appearance before the grand jury had not been a success. While Mr Clinton had professed to be looking forward to testifying "truthfully and fully", Mr Kendall announced curtly afterwards that his client had testified "truthfully".
The omission, it transpired - from Mr Clinton's awkward four-minute "admission" on television three hours later and most recently from the completed report of the independent prosecutor, Kenneth Starr - covered his antipathy towards his accusers, his petulant evasiveness on the nature of his activities with Ms Lewinsky, his legalistic hair-splitting on definitions of sexual contact and his fury that such subjects were even broached.
The video tells all. Specifically, it shows that the President - a man hailed for his dignity under political and personal attack, acclaimed for his natural affinity with people of all ages, races and stations of life, and seen in public as always affable and even-tempered - also has a nasty side.
This encompasses a short temper, flashes of extreme anger, impatience with individuals whom he believes have let him down and a tendency to sulk when things do not immediately go his way. The obverse of his mastery of the political art is a talent for manipulating those close to him. His quickness of wit and intellectual scope are matched by an arrogance towards those he deems inferior in argument, but are transformed into pedantry and terminological point-scoring if ever he is cornered. The cultivated sophistry of the lawyer that Bill Clinton was trained to be exists side by side with the boorish conduct and linguistic coarseness of the Arkansas tap-rooms where his stepfather drank his life away.
His political history is littered with evidence of his seamier side: there were the deals he made in order to escape call-up for Vietnam (and go to Yale law school); the multifarious explanations he later offered for what he had done; his partial admission of pot-smoking, famously, without inhaling. His career is also flecked with hints of a ruthlessness towards those who stand in his way. Rarely, though, can threats or intimidation be traced directly to Bill Clinton.
His several biographers, in common with some of his closest associates from his Arkansas years, see the seeds of his predicament clearly present in his past: from his capacity to inspire loyalty, to his manipulative streak, to his philandering and his streetfighter instincts when under pressure. Their surprise is only that, having achieved his life's ambition, to reach the White House and use the office for liberal change, he could be so thoughtless, arrogant, or (the word most commonly used) reckless, as to place that achievement at risk.
As candidate and then as President, he has (with one recent lapse in a televised argument with an opponent of "affirmative action") successfully cloaked his intellectual arrogance in an amiable talk-show manner. He has eschewed all crudeness of behaviour and language in public, assuming the manner of a "little boy lost" when occasionally caught out. During his first presidential campaign, the almost shy evasiveness of his answer to allegations about an affair with Gennifer Flowers - "I caused pain in my marriage" - was regarded as more endearing than dishonest.
Reporters and aides who followed that campaign, and the many campaigns he had already fought in Arkansas were under few illusions. Tales abounded of his incorrigible womanising, rages, shambolic organisation, buck- passing and - yes - lies or near-lies told to conceal failings.
Yet, as in Joe Klein novel Primary Colours, a thinly veiled account of the 1992 campaign, his allies and aides made their compromises and worked for his victory. They believed the Clinton cause and his New Democrat policies outweighed his personal failings.
The Lewinsky affair has caused a few of his staunchest allies to defect. Among them are two of his earliest presidential spokesmen, George Stephanopoulos and Dee-Dee Myers, who continued to be his articulate advocates even after they left his employ. But they knew him all too well. Mr Stephanopoulos was one of the first to voice his suspicion that the denials of his relationship with Ms Lewinsky might have been less than forthright; Ms Myers announced her defection immediately after his 17 August admission, which she deemed inadequate and ill-judged.
Many others, however, like White House communications director, Ann Lewis, and members of his Cabinet (not one of whom has so far resigned over the Lewinsky affair) have stuck to their personal compromises and stood by him. "Disappointed", they may be, but they still have sufficient faith in the cause, or sufficient trepidation about cutting adrift, to remain.
The great imponderable is how the American public will respond when the videotaped testimony is broadcast tomorrow and they see with their own eyes the nasty side of their President in all its gauche dishonesty and hurt dignity. They have had hints of it - in that little lapse with Prof Abigail Thernstrom over "affirmative action", and in Mr Clinton's continuing friendship with Dick Morris, his first campaign publicist and a gifted charmer very much of the Clinton ilk. Mr Morris, a married man, left the President's team after being caught with a prostitute, but he was still the first in whom Mr Clinton confided after the allegations about his involvement with Ms Lewinsky emerged.
Mostly, though, Americans know little of his other face. They preferred the outgoing populist of former years to the reticent, legalistic President they have seen since January. But the lawyers and Dick Morris's polls told him that full confession, at least back then when the Lewinsky allegations were fresh, would be the greater risk, and the lawyer in Clinton knew better than to argue.
Tomorrow's broadcast - a surreal cross between televised trial and nationwide referendum - presents at once the greatest threat to his presidency and a chance for his survival.
Will Americans switch off their televisions and refuse to countenance the humiliation of the man they elected? Will they watch and pay him the compliment of "feeling his pain" - the pain of a citizen like themselves caught in an embarrassing web of his own weaving? Might they project their disgust on to Kenneth Starr, the uppity prosecutor who demeaned the presidency? Or will they decide that their loyalty has been exhausted, and call off the compromise? In making their choice, Americans will decide Bill Clinton's future, and their own.Reuse content