And the Conservatives paid a price for failing to get the right answer in 1997, 2001 or 2003. On each occasion, Labour feared Kenneth Clarke the most, and on each occasion the Conservatives would not have him as leader, mainly because he was pro-European. Having got the answer wrong three times, the solution now being urged on the Tory party by an enthusiastic press has the deceptive attraction of simplicity.
Kenneth Clarke would have been the right answer the last three times - he must be the right answer now. But what if the answer to the question has changed? It was all very well in 1994. The opinion polls were clear: Tony Blair was the most powerful anti-Conservative weapon at Labour's disposal. The polls are not so clear now.
Indeed, they were not all that clear in October 2003, when Tory MPs deposed Iain Duncan Smith. Clarke was not a serious contender then because his views on Europe would have turned the Tory party back into a cartoon playground brawl starring such cartoon characters as Wild Bill Cash and John "The Vulcan" Redwood. Most Conservative MPs calculated that the losses would have outweighed the gains from the centre ground of a Clarke leadership. The default assumption in Labour circles remained that Clarke would do best against them - but because it never seemed likely, it was never considered very deeply. Blair always had the luxury of knowing that, because of its obsession with Europe, the Tory party lacked the discipline to do whatever it took to win.
It has taken a further election defeat to force the Tory party to the point where it may be willing to ask itself the important question. Clarke said yesterday, as much in hope as analysis, that the party has changed in the past four years. Certainly his promise to deliver Liberal Democrat and disillusioned Labour supporters sounded more compelling than David Cameron's vapid ambition to make Britain "the most civilised place in the world to live".
The paradox is that it is no longer obvious that Clarke is the answer to the Tory party's question. And it is no use asking Labour politicians who they are most afraid of, because they cannot be relied on to give an honest answer. Tony Blair once said he thought it was the Tory party's "biggest mistake" to have got rid of Margaret Thatcher. This was despite the overwhelming evidence that, had she stayed, she would have lost the election that John Major won in 1992.
But Blair's purpose was to contrast his own mock-Thatcherite style of decisive leadership with Major's drift after 1992.
This time, of course, it is not Blair's opinion that matters, but Gordon Brown's.
Whoever takes over as Leader of the Opposition will probably be up against Prime Minister Brown in 2009, so the match-up that matters is a mirror image of 1993-97, when Brown shadowed Clarke as Chancellor. It would be right to be sceptical about the claims of Gordon Brown's supporters that they find it hard to rank the Tory leadership candidates in order of preference. Equally, however, it may be that they are telling the truth when they say that none of the Tory hopefuls stands out as a particular threat.
Certainly, some Labour minds have been looking out for a big shift in European policy to dramatise the message that the Conservative Party had changed. When he was still Minister for Europe, Denis MacShane once told David Cameron that whoever made the first move on Europe would mark themselves out as the far-sighted candidate in the next Tory leadership contest.
So it has proved, although not quite in the way MacShane expected. The first big policy shift of the Tory campaign did not come from one of Thatcher's children symbolically breaking with the party's fierce anti-Europeanism. It came from a paleo-European moving in the opposite direction, when Kenneth Clarke said that the European constitution was dead and the question of Britain adopting the euro was in cryogenic suspension. But MacShane's larger point holds. Simply choosing Clarke as leader would be powerful evidence that the Conservatives had become a more inclusive party again.
Clarke has other selling points too, and he set them out with typical chutzpah this week. Yesterday, he stroked the anti-war prejudices of the liberal media by repeating his opposition to Britain's part in the invasion of Iraq - while trying to balance it by saying: "I had previously supported every war embarked upon by a British government." But it was a bit of backward gesture, of little immediate consequence, because he does not advocate troops out now. It might give him some good lines against Blair, but it is unlikely to inflict serious damage on Brown.
Perhaps it should, as the Chancellor's position is the most dishonourable if, as is often implied, he privately thought the war a bad idea but supported it in public in order to advance his own political interest. In practical politics, however, Brown is just as likely to benefit from not being Blair as Clarke is.
Equally, Clarke might hope that his opposition to the war will bolster his reputation for good judgement, as when he was vindicated in resisting the Bank of England governor's advice to raise interest rates in 1997. He has a good claim but, as it turned out, Brown's coup de theatre of making the Bank independent stole all the plaudits.
And Clarke's negatives remain poisonous. His job as a tobacco salesman is electorally carcinogenic. Spluttering about the "puritanical tinge" of attitudes to cigarettes cannot change that. It is also instructive to note, as Michael Portillo did last weekend, that Clarke has not given up his deputy chairmanship of British American Tobacco - he has merely said that he would if (he corrected it to "when") he became Tory leader.
Most damaging of all, though, is the fact that Clarke would be the candidate of the past. This is nothing to do with his age. It is to do with his association with the Thatcher-Major years, coupled with a certain inflexibility of his outlook. And that is a defect of Clarke's repeated candidacy that gets inexorably worse with the passage of time.
Gordon Brown finds himself in the unexpectedly happy position of facing a Conservative party that is finally prepared to ask itself the right question - who does Labour fear? - just when the answer becomes impenetrably cloudy.
The writer is chief political commentator for 'The Independent on Sunday'Reuse content