As resentments swell, the imperative for a joint ticket could overwhelm other factors that nominees customarily consider in choosing a running mate — including tapping someone with whom the nominee has good relations. In 1980, despite frosty feelings, Ronald Reagan put primary rival George H.W. Bush on the ticket in a pragmatic political move.
Normally, nominees have "the flexibility to decide who their running mate is going to be so they're comfortable with that running mate, and that person meets their particular political and substantive needs," Panetta says. "But in this situation, if in fact the party is divided, if there's a danger that important constituencies may break away — the only way to hold them together may be to have both of them on the same ticket."
'An almost unstoppable force'
The topic already has caused friction between the two camps.
Two weeks ago, Bill Clinton suggested that his wife and Obama would be "an almost unstoppable force" if they joined together — presumably with Hillary Clinton in the lead spot.
"If you can unite the energy and the new people that he's brought in and the people in these vast swaths of small-town and rural America that she's carried overwhelmingly, if you had those two things together, she thinks it'd be hard to beat," Bill Clinton said while campaigning in Mississippi.
Obama accused the Clinton campaign of "hoodwinking" voters by suggesting he wasn't ready to be commander in chief while simultaneously floating the possibility of a joint ticket. "That's exactly the kind of doublespeak, double talk that Washington is very good at," he said. Obama noted that he, not Clinton, held the lead in pledged convention delegates.
"I want everybody to be absolutely clear: I'm not running for vice president," Obama said. "I'm running for president of the United States of America."
Obama supporters were outraged by the suggestion he should take the No. 2 spot, says Joe Madison, who heard from them on his radio talk show. His program is carried on Washington's WOL-AM and syndicated on XM Satellite Radio.
"For her to suggest that Obama would be a good running mate is an insult because, one, she's behind in the delegate count, and she can't offer what she doesn't have," Madison says. "What you end up doing is undervaluing, underestimating and marginalizing Obama's status as the front-runner."
The idea of an Obama-Clinton ticket has its own hurdles — for one, whether the 60-year-old New York senator would be willing to accept the secondary spot to a rival 14 years her junior. For another, what complications might arise for a new president in having a former president as the vice president's spouse. "You have to wonder," University of Pennsylvania political scientist Richard Johnston says.
Still, neither candidate has flatly rejected a joint ticket, even as Obama's campaign questions Clinton's honesty and the Clinton camp portrays Obama as unready. Obama campaign manager David Plouffe and top Clinton strategist Mark Penn both refused to discuss the issue, calling it premature.
"We'd have some inevitable questions," Pennsylvania Gov. Ed Rendell told reporters after a Clinton rally in Scranton, Pa., this month. " 'Sen. Obama, you said Sen. Clinton wasn't trustworthy; how can you make her vice president, one heartbeat away?' 'Sen. Clinton, you said Sen. Obama is not ready to meet the challenge of national security; how can you put him one heartbeat away?' "