Hillary and Bill Clinton have said that Barack Obama would be a strong running mate on a Democratic presidential ticket headed by the former first lady.
In talking up a joint ticket, the Clintons may be seeking to put Hillary in consideration for the top of the ticket when she so far has failed to win the votes necessary to assure that she would face Republican presidential candidate John McCain in the November election.
The manoeuvre may also be aimed at countering an image in voters' minds of Mr Obama as presidential material and at helping restore an aura of inevitability as the party's nominee that Mrs Clinton had early in the campaign.
The Clintons had previously derided the first-term US lawmaker as inexperienced,
Former Senate Democratic leader Tom Daschle of South Dakota, an Mr Obama backer, mocked the idea. "It may be the first time in history that the person who is running number two would offer the person running number one the number two position," Mr Daschle said.
Mr Obama leads Mrs Clinton, a fellow Democratic senator, in the Democratic nomination race,
but neither is likely to reach the 2,025 delegates needed to become the nominee in the remaining state-by-state contests.