Will Gordon Brown be Britain's equivalent of former President Gerald Ford? The late US President made constitutional history by becoming the only holder of that office never to have been elected by the people (or, for constitutional purists, by the electoral college). Indeed, he was not even elected on a Vice-Presidential ticket at the previous presidential election in 1972.
When Richard Nixon's Vice-President, Spiro Agnew, resigned in disgrace, Mr Ford, a congressman and leader of the Republican majority, was appointed to the post by Nixon before taking over the White House himself in August 1974. But he failed in his bid for re-election, in his own right, in the subsequent presidential election in 1976, losing to Jimmy Carter.
The obituaries for Mr Ford must send a shiver down Mr Brown's spine as he contemplates the business of becoming Prime Minister without the endorsement of the electorate. The British precedents are many but the fortunes of being elevated to the premiership by changes in mid-term are mixed. John Major took over in November 1990 and ran out the parliamentary term almost until the end of the full five years, narrowly squeaking a victory in the spring of 1992.
The Labour Opposition made little fuss about his governing for 18 months without a "people's mandate". The palpable sense of relief among the voters at the departure of Margaret Thatcher transformed the Tories' poll ratings almost immediately, and Major was able to exploit his personal popularity in the wake of the first Gulf War.
Many of us, myself included, urged him to seek an early endorsement by the voters in the spring of 1991, when that parliament, already four years old was beginning to run out of legislative steam. Major resisted on two grounds. First he was determined not to be accused of holding a "khaki" election off the back of the military success in recovering Kuwait from the Iraqis.
He also wanted to ensure that the hated community charge, or "poll tax", was repealed by Parliament before an election was held so that it was clear that the decision to implement the council tax was more than an empty promise. The tactic worked so well that local government finance had, to some extent, lost its electoral toxicity by polling day. Major was also determined to present the Maastricht Treaty, signed but not ratified, before the election as the basis of a truce within the Tory party which would not damage its prospects as an election issue. Pro-European Tories could say they believed in a single currency, while Eurosceptics could present the "opt out" arrangements as a triumph of the new Prime Minister's negotiating skills.
It was a close-run thing, with the election successfully completed before the ERM débâcle six months later. But Major had secured his own mandate. The case for playing the election long was vindicated and the change in personal style showed voters that there had been a new government for 16 months.
Other precedents for changing horses within a governing party in mid-term are mixed. Sir Alec Douglas Home and James Callaghan both became Prime Ministers but failed to win a subsequent general election. Even the great Winston Churchill, after five years in Downing Street without the peoples' ratification, failed to win two subsequent elections (1945 and 1950) and managed only once - in 1951 - to secure his own mandate.
The two alternative precedents Mr Brown (assuming it is he) will be studying closest will be those of Sir Anthony Eden, who succeeded Churchill, and Harold Macmillan, who himself succeeded Eden almost exactly 50 years ago. Eden became Prime Minister three and a half years into the parliamentary term, and called a general election immediately. Eden, like Brown, had been the heir apparent for years, and secured an increased majority in one of the easiest election campaigns of modern times. But the victory turned to ashes thanks to the Suez débâcle a year later.
Macmillan led the Tories, after Eden's resignation, for nearly three years without his own mandate, before calling a successful general election in 1959 and being returned to office with an even bigger majority. Like Brown, Macmillan had been Chancellor and was assumed to have been against the Suez invasion all along. He used the threat of financial crisis, which he implied would be precipitated by the invasion, as a means of leverage against Eden, with many believing Macmillan to be plotting his way to Number 10 all along.
So Mr Brown's dilemma is whether to follow Eden, Macmillan or Major in order to avoid ending up like Home or Callaghan. Nothing beats a party leader, however, who arrives fresh-faced in 10 Downing Street from the leadership of the Opposition. This task may be the most thankless and difficult in British politics, but the appointment of a new Prime Minister, whose previous job was Leader of the Opposition, gives them an immediate authority and security.
Wilson, Thatcher, Blair - and even Edward Heath - began their first day in office with the cheers of the voters ringing in their ears. Whatever fist Mr Brown makes of his first 100 days or year, the anticipation of the date with the voters will overshadow every one of his decisions. By contrast, Prime Ministers whose removal vans arrive to the cheers of a grateful electorate are instantly freed from the need to consult the opinion polls - at least for the first year or two.
Wilson, Heath, Thatcher and Blair could immediately trash all their immediate predecessors in Downing Street. Everything inherited in the pending tray can be dumped if necessary. But a new Prime Minister presiding over the same party in power cannot escape the shadow of the immediate past. The blame game must be more subtly played.
Iraq will be the issue most likely to cause the new Prime Minister the greatest angst. Dare Mr Brown signal a significant change of approach and contemplate a break with Washington? Polls and Labour Party activists are certainly looking for such a signal. But inheriting a legacy, however poisoned, that still has to be defended offers little opportunity for a fresh start. Unpopular policies can only be renounced by stealth, except in circumstances such as Major's public abolition of the poll tax.
Gerald Ford's accidental elevation to the presidency meant that little was expected from him. "I am a Ford, not a Lincoln" was his famous comment at the time of his swearing of the oath of office. Brown must show middle-class Tories that he is not red. But can Brown be green? This will also be a question that dominates his premiership if David Cameron has his way. Brown hopes for a coronation, but that cannot properly occur until he secures his own mandate. Only then will he be entitled to the inauguration that eluded President Ford.