No discussion about possible presidential nominees gets far without the words "vice president" turning up. John Edwards doesn't seem quite up to the task of beating Hillary Clinton or Barack Obama, but how about nominating him for vice president again (as in 2004)? Or, if Clinton is the nominee, might she feel obligated to name Obama instead (or vice versa)? And, over on the Republican side, if McCain gets the Republican nomination, who should be his running mate? One may wonder whether Mitt Romney, or even Rudy Giuliani, would be willing to accept the second spot; and anyway having two white males on the ticket might seem too much of a muchness in 2008, especially if the Democrats are adventuresome. But how about Condoleezza Rice?

Don't kid yourself that the vice presidency is too trivial a post to contend for, however much a person may claim to spurn it. The average politician would kill for a chance at it. Serving four years in supremely comfortable surroundings while just one heartbeat from the presidency is the ultimate dream job. For one thing, its sheer prominence laid the foundation for five vice presidents to go on to the presidency. And the death of the president, through ill health, an assassin's bullet or resignation put nine others in the Oval Office without even having to run for it. Added together, that's a third of America's presidents. It's true that some people (like Romney and Giuliani, mentioned above) have held political positions so high, or acquired reputations so formidable, that the vice presidential nomination might at first seem too trivial for them to consider. But you can be sure that even they would think long and hard before declining the offer.

The first impulse, in considering who should receive the vice presidential nomination, is usually a sentimental inclination to choose the big loser for the top spot. Thus, as noted above, if Hillary wins the Democratic nomination, Obama springs immediately to mind for the vice presidency. Similarly, if McCain is the Republican choice, his chief rival -- Romney, say -- will be touted for second place. But these automatic reactions don't necessarily prevail. Would the Democrats, having scored a first by nominating a woman for the presidency, be eager to double their bet on novelty by naming an African-American for the vice presidency? Or would they be wiser to pick a more conventional choice, like Edwards or Bill Richardson? The Republicans, conversely, if they name McCain or Romney for the presidency, may be on the lookout for a more original selection for vice president -- perhaps Rice, as suggested above.

In any case, you can be sure that the two presidential nominees will have only one question on their minds: Who can add most to the strength of the ticket? Sentimentality ("Let's pick Joe -- he was with us from the start") will have nothing to do with it. Conceivably the job may have been bargained away in the battle for the nomination, but this was likelier in the good old days of smoke-filled rooms than it is now, when primaries choose most of the delegates.

So the question of the vice presidential choice is almost sure to involve, in both parties, who can do the most for the ticket. In the case of the Democrats, however, there is certain to be a powerful inclination to give the spot to Obama -- not because he fills that bill, or even because he was (in our hypothesis) the chief defeated contender for the nomination, but because, as an African-American, he represents such a powerful bloc in the Democratic Party. It is well known that African-Americans vote overwhelmingly Democratic, but it isn't always appreciated how large a force they are in a Democratic convention. A third, or even more, of the delegates are likely to be African-Americans.

The result may be that the Democratic ticket will seem, as already suggested, heavily tilted in favor of two of its biggest voting blocs: feminists and blacks. And that may not be an advantage in November.

For the Republicans, the problem will be how to add a little flavor to a ticket that otherwise may seem a bit too plain vanilla. Is there a woman or a "person of color" somewhere in the Republican portfolio who could do the trick? Clearly, in both parties, the selection of a vice presidential nominee is going to be an important consideration.