Moderator Wolf Blitzer of CNN asked whether each would consider choosing the other as vice-presidential nominee. The mere question was met with thunderous applause by the live audience (which consisted, we should bear in mind, of intense partisans of one candidate or the other). And there is a history in US politics of seemingly bitter primary-season rivals burying the hatchet for the sake of the party and pretending they like each other for a few months. John Kennedy's selection of Lyndon Johnson as his running mate in 1960 is the most notable example.
Both candidates ducked the question, making jokes and dismissing such talk as premature. But neither said no, and ever since not a few Democrats have been thinking - and dreaming.
But I suspect they're in dreamland. Let's say Obama wins the nomination. The question that pops to mind is: why would he, or anyone, choose as his vice-presidential nominee a polarising and controversial running mate?
Running mates are supposed to do three things. First, they are supposed to understand that the presidential nominee calls the shots. Their job is to travel the country for four or five months singing not their own praises but the nominee's. Can we really expect - and I say this in Clinton's defence - America's most admired woman (and she is that, in poll after poll) to play such a subordinate role? On areas of policy, will Clinton suddenly be able to adopt Obama's position - saying, for example, after denying it for more than a year, that the Iraq war was indeed a mistake?
Second, running mates are supposed to bring some geographical advantage to the ticket. Kennedy chose Johnson, in spite of their mutual nuclear contempt, because LBJ would help nail down Texas and the south. I'm not sure Clinton brings Obama a single state he can't get without her.
Third, running mates ideally have strengths that make up for the candidate's weaknesses. George Bush was weak on global and military experience. Dick Cheney, a former defence secretary who had overseen a successful war, was a strong choice by Bush, whatever we may think of how that has turned out.
One can make a symbolic argument for Clinton on this point. He is black and male, she is white and female. But she doesn't have many substantive strengths that he lacks. Obama would be better off with someone with global and military credentials - a Democratic Cheney, without the Dr No hunger for world domination.
The opposite case? Obama is a somewhat more plausible choice for Clinton than she is for him, because he has greater appeal to independents. But here, too, on my three criteria, Obama doesn't bring Clinton enough that she doesn't already have on her own. He may have become, like her, too large a figure to play second violin. He doesn't bring her a state that I can see, and he doesn't add much substantively.
Finally, asking Americans to vote for a woman or a black man is one thing; but asking them to vote for both? I would like to think my country has changed that much.
If I were advising them I'd push each toward a white man from a state or region where they may have the potential to pick off crucial or unexpected electoral votes.
The Everly Brothers said all they had to do was dream. My guess is that Democrats will have to do a little more.
