In past presidential nomination battles, runners-up have bargained for different things.
Some have asked for help in retiring campaign debt or for a space on the ticket as the vice president — which may explain why New York Sen. Hillary Clinton insists on remaining in the Democratic race.
Both Illinois Sen. Barack Obama and Clinton have been asked about the idea of a unity ticket many times. The tone of their answers is always the same: friendly but noncommittal.
At least one top Clinton adviser has said privately that the New York senator would jump at the chance. Clinton's communications director, Howard Wolfson, was less enthusiastic.
"I've seen no evidence of her interest in it," he said. "And I think any talk of it is premature."
Obama Plus Clinton — the 'Perfect Candidate'?
But Democratic voters are talking about it. The latest Quinnipiac poll shows three out of five of them like the idea.
"There's a lot of people out there, millions of voters, that would love to see that ticket," says Steve Jarding, a Democratic consultant unaffiliated with either campaign.
"We've heard it a lot through this campaign," he adds. "If we could just get some of Hillary's experience and some of Obama's freshness, boy, we'd have a perfect candidate. We can't combine the two into one person, but we can combine the two into one ticket. I don't think it's that far-fetched."
Former New York Gov. Mario Cuomo thinks it makes practical, political sense.
"Obama cannot win against McCain without almost all of the votes that Hillary Clinton is getting from her separate, distinct constituency and vice versa," Cuomo says. "And she can't win — if she were to be successful by some small miracle — without most of the votes that Obama is getting."
"You don't have to be a Wall Street genius to know that calls for merger," Cuomo adds.
But Would a Unity Ticket Win the Swing Vote?
Phil Bredesen, the Democratic governor of Tennessee, has a different view.
"I honestly believe that probably each of the candidates, if they were the nominee, ought to find a VP who brings something that moves them to middle," he said. "They both need some people who can help get that middle 10 to 15 percent that is going to be the swing vote that will determine who the next president is."
Strategist Mark Mellman, also unaffiliated with either candidate, says there are other reasons why it might not be such a dream ticket after all.
"I think there's going to be a lot of pressure to put this unity ticket together," he said. "People use the VP pick in different ways, but most often, it's to send a message. Sometimes that's a message of balance — geographic or ideological balance. Sometimes it's a message of reinforcement. When Bill Clinton picked Al Gore, he was really reinforcing the message of young, progressive Southerners together on the ticket."
The message Obama wants to reinforce, of course, is change. People familiar with the thinking inside the Obama campaign say Clinton has too much baggage.
And then there's the question of what role former President Bill Clinton would occupy. Massachusetts Sen. Edward Kennedy, a prominent Obama supporter, said he did not think a joint ticket was possible.
"I would hope that [Obama] would also give consideration to somebody that is in tune with his appeal for the nobler aspirations of the American people," Kennedy says. "And I think if we had real leadership — as we do with Barack Obama — in the No. 2 spot as well, it would be enormously helpful."
The country is still a long way from finding out whether Clinton would even want the No. 2 slot, or if Obama would offer it to her. In the meantime, Cuomo is hopeful that the dream ticket could come true.
"For all you people who say it couldn't happen — really?" he says. "Look at all the things that happened already in this campaign that couldn't happen."