By James Coomarasamy
BBC News, Washington
Only Barack Obama and Hillary Clinton know the contents of their intimate fireside chat on Thursday evening, at the Washington DC home of Senator Dianne Feinstein.
Could Mrs Clinton help Mr Obama with working-class white voters?
Neither camp has released any details about the hour of calm they spent away from the fevered speculation about a possible joint ticket, in - somewhat ironically - each other's company.
As they sat in those comfy chairs, they would have been engaging in a subtle, political dance, whether or not there was any specific discussion about the vice-presidential issue.
For Barack Obama, the challenge is clear.
He needs to keep, or get on board, the 17 million Democrats who voted for his rival in the primaries, while establishing his authority as the new, effective leader of the Democratic Party.
So - does he embrace Senator Clinton or keep her at a distance?
For the moment, he is trying to do a bit of both - meeting and praising his former rival, while stressing that he will not be rushed into picking a running mate.
He does not want the "Hillary issue" to overshadow the campaigning against Republican John McCain, which has already begun in earnest.
Many Democrats... believe Mrs Clinton mishandled the moment on Tuesday evening, by failing to acknowledge Barack Obama's historic win
Yet, at the same time, Senator Obama knows that the person best placed to deliver those Clinton voters is Hillary Clinton herself.
The signals that she gives - especially to those white, blue-collar Democrats who have yet to warm to the party's presumptive nominee - will be important.
Senator Clinton may have lost the contest, but she is - in some ways - in a stronger position than ever.
So, Saturday's endorsement is important.
It marks the moment when Mrs Clinton transforms from campaigner into cheerleader.
As most Democrats acknowledge, it will not be an easy transition, especially after such a long and intense battle, which she was heavily favoured to win.
But that is the reality she is having to face.
Work to do
How she handles it - especially in these early phases - will set the tone for her future political career, and it could well have an impact on Senator Obama's chances in November.
The New York senator already has some work to do.
Many Democrats - even some of her closest supporters - believe Mrs Clinton mishandled the moment on Tuesday evening, by failing to acknowledge Barack Obama's historic win.
And the Obama campaign has not been impressed with the public efforts being made by some of her supporters to get her onto the ticket.
And what about Bill Clinton?
His prospective presence in the White House is often cited as a reason for Barack Obama not to pick Senator Clinton as a running mate.
It will be much harder for him to deliver a message of change, the argument goes, with a former first couple on the ticket.
Yet, for all the criticism of the former president's role in the campaign, he too remains a popular figure within the Democratic Party.
Barack Obama may have beaten the Clinton machine, but he cannot escape the Clinton factor.