The decision to wear a tie can be a sartorial minefield for politicians and the public alike, says historian David Cannadine.
The former governor of the state of New York, Mario Cuomo, once observed that in a modern democracy "you campaign in poetry but you govern in prose".
Translated from speech to dress, the attire of Britain's party leaders for the televised debates during the general election of 2010, or of the candidates currently seeking the Republican Party's nomination, or of President Barack Obama when he goes out on the stump, suggests that you campaign wearing an open neck shirt, but govern wearing a tie.
To press the flesh and get yourself elected, it seems essential to dress down and appear casual, like ordinary voters, rather than be buttoned up or formal.
But to undertake the very different task of running a country, it's still expected that politicians will wear what is termed business attire, which means a suit (whether you are a man or a woman) and also a tie (if you're a man, or if you were Margaret Thatcher as depicted in her caricature from the television series Spitting Image).
But the conventions as to when it's essential to wear a tie and when it's acceptable not to, have often been a sartorial minefield, as I discovered to my cost during the late spring of 1974, when I was finishing a year as a graduate student in the United States.
Luckily for me, my stay had coincided with the enthralling drama of what became known as the Watergate scandal, which had begun with the arrest of five men for breaking into the headquarters of the Democratic National Committee, as part of a campaign mounted by some Republican zealots to ensure the re-election of President Richard Nixon.
That had occurred in the autumn of 1972, but it was later alleged that Nixon had known about the burglary, and was complicit in the cover-up that followed, and as a result he was compelled to resign the presidency in August 1974.
The building where the break-in occurred was in a recently constructed hotel and apartment complex, located in the part of Washington DC known as Foggy Bottom, and because it bordered on the Potomac River, it was named the Watergate.
As the scandal unfolded, the Watergate became a major tourist attraction for those who wanted to see where the train of events had begun that would end in Richard Nixon's disgrace. During the late spring of 1974, I was visiting some friends in Washington, and I made my own pilgrimage there one evening.
I went into the bar of the Watergate Hotel, and asked for a drink, but the bartender refused to serve me because I wasn't wearing a tie.
Summoning up such limited dignity, lame repartee and righteous outrage as I could muster, I replied that the Watergate bar must be the last place in the world just then where it was either appropriate or plausible to lay down exacting rules as to how people should behave or what they should wear.
But my protests were to no avail: I never did get my drink, and although the Watergate complex later acquired a more respectable fame as the place where many members of Ronald Reagan's administration chose to live, the Watergate Hotel subsequently closed down.
My unhappy encounter there was surprising because America has always seemed more casual and relaxed about matters of dress than Britain, having rejected knee britches and cocked hats, along with hereditary titles, as degenerate symbols of the royal and aristocratic world of Old Europe in 1776.
And since the rebellious and un-deferential decade of the 1960s, dress codes had been becoming ever more informal across much of the western world, for it wasn't only among rioting students that jackets and trousers and ties (and short hair) were deemed to be 'out', while jeans and tee shirts (and long hair) were welcomed as being 'in'.
And for those who wished to appear without a tie, but well-dressed in a style that would become known as radical chic, there were the high-collared jackets made famous by Nehru or Mao Tse Tung, or the turtle necked sweaters popularized by Senator Robert Kennedy, that could be worn instead.
This meant that by the time of my unhappy encounter in the Watergate Hotel bar, men might not have been wearing ties for a variety of different reasons, even if they all seemed the same to the hotel staff.
I had chosen to go without a tie that evening because I was on holiday and the weather was very hot and humid, and I was wearing informal clothes that were appropriately casual and comfortable.
But for other people, especially the student revolutionaries of my generation, refusing to wear a tie was not so much a matter of personal convenience, but an ideological statement and a political act: for it meant a deliberate rejection of authority in all its forms.
Che Guevara didn't wear a tie, nor did Fidel Castro, and Albert Einstein had never really liked them, either. All his life, he had a horror of constraint, be or physical, intellectual or emotional, which he described in the German word "zwang". For Einstein, as for many of the student revolutionaries of the 1960s, the necktie became the very embodiment and symbol of "zwang".
There was some justification for this view, well summed up in the phrase "the old school tie", which was - and in some quarters still is - redolent of snobbery, elitism, connection and privilege.
For ties in their most traditional form, with diagonal stripes or heraldic crests, were closely associated with public schools, Oxford and Cambridge colleges, and gentlemen's clubs such as The Garrick or the Marylebone Cricket Club, better known as the MCC, and they could only be worn by old boys or alumni or members.
Lower down the social scale, ties had become more widespread from the late 19th Century with a massive growth in the number of clerks and bureaucrats and petty officials who were revealingly described as white-collar workers - and in those days, you couldn't wear a shirt with a white collar unless you were wearing a tie as well. And after World War I, there was a significant proliferation of striped regimental ties that could only be worn by those who had recently been on active service.
Depending on its design, wearing a tie in Britain might mean that you were a humble office worker, or that you belonged to one of the closed worlds that formed part of the establishment.
But in the United States, diagonally-striped ties became the widely accepted dress code for professionals and for those who worked on Wall Street. They were produced in many different colours and many different permutations, and they were especially associated with the firm of Brooks Brothers, which by the 1920s was specialising in outfitting professional American men.
In order to distinguish their product from the exclusive British club and regimental ties on which they were modelled, the Brooks Brothers ties were manufactured with the diagonal stripe going the other way, and to this day, striped American and British ties retain this difference.
In the years since my unhappy encounter at the Watergate Hotel, I've worked - and bought ties - on both sides of the Atlantic.
For much of the 1990s, I taught history at Columbia University in New York, and unlike many of my more radical professional colleagues, I invariably wore a tie when I lectured. Some were striped, but most of them were more vividly patterned and highly coloured. Although they never rivalled those of certain newsreaders, they did attract some attention in the classroom.
At the close of each semester, the students were asked to fill in evaluation forms, and to comment on the content and delivery of the lectures, and the amount and appropriateness of the assigned reading.
At the end of the forms, there was a small space to add any further observations about the lectures or the lecturer. Few of my students ever did so, but on one of the forms, which I have treasured ever since, were written just two brief words, followed by an exclamation mark: "Nice ties!"
If ever the Watergate Hotel reopens, I might go back to its bar and try to order another drink; and if I do so, I'll be sure to take that piece of paper with me although I am still undecided as to whether I should wear a tie.