All parties face a dilemma in picking a standard bearer for elections. The brutal truth is that often the candidate most popular to the members may also be the most unelectable. And so party bosses constantly remind the rank and file of the need for electability.
In the US, because the primary system embroils a mass electorate in the choice, the problem is the central challenge of the political system, a point driven home vividly by a Zogby poll on Tuesday as senator Barack Obama launched his candidacy (although, technically, his announcement that he was setting up an exploratory committee was merely a dress rehearsal). The poll found that 46 per cent of respondents said they would vote for party change in the White House, while 29 per cent said they would vote Republican. Asked if they approved or disapproved of the way President Bush is handling his job, 62 per cent disapproved. But what will drive party bosses to despair was the finding that just 6 per cent said it is more important to them to nominate a candidate who can win, while a massive 92 per cent said it is more important to choose "a person who represents my values and issues".
Currently senator Hillary Clinton, also not formally declared yet, almost straddles both camps happily - a recent CNN poll put her clearly ahead of Obama among Democratic voters, 28 to 17 per cent. Asked how they would vote in a presidential contest between Ms Clinton and the most likely Republican candidate, senator John McCain, the latter came out on top by an insignificant 48 to 47 per cent. Against Obama, he took it more comfortably - 49 to 40 per cent.
It is early days, of course - the Iowa caucus, the first of the primaries, will be held a year from this week. And Mr Obama (45) has a special wow factor. The son of a Kenyan father and Kansas mother, and only the third African-American in the US Senate since Reconstruction, he is a powerful, inspirational speaker who outshines almost anyone in US politics today and reaches across racial boundaries. He has never played racial identity politics. (Indeed, it is striking that the two front-runners in the Democratic camp may well be blazing trails for their ethnic or gender communities, but neither has been a torch carrier for them).
Mr Obama's politics will appeal to the rank and file; he is a liberal on touchstone issues like abortion and opposed the war early. But he is vulnerable to the charge of inexperience. Although likely to be able to put together a fund-raising team that can rival the Clinton machine - they say a candidate will need to raise $35 million this year to be in with a chance next year - there are also at least five other contenders in the Democratic camp. These include former vice-president contender, John Edwards, a formidable campaigner - and a southerner - who has built a strong constituency in the unions and among ordinary party members on poverty issues.
Which all makes for one of the most interesting primary seasons in years.