By Nick Bryant
BBC News, Washington
Mr Obama has spoken of his strong bond with his maternal grandmother.
A death in the family on the eve of Election Day. After the deftly-worded condolences comes the gently-whispered question: what will be the impact on the race?
Or, put another way, what are the politics of this personal bereavement?
Certainly, it has meant that Barack Obama's final appearances have been loaded with more emotion. In Charlotte, North Carolina, it was a teary-eyed candidate who paid tribute to his grandmother. Gone was the winning grin that he wore earlier in the day.
In paying tribute to "quiet heroes" like Madelyn Dunham, he demonstrated once again the skill that has put him on the verge of such a breakthrough victory: his singular talent with words.
He spoke, too, of the importance of traditional, core family values, possibly blunting the Republican critique that he comes from outside the American mainstream.
Race question neutralised
As I write, Lou Dobbs is on CNN, saying that not much is known about Barack Obama's background, and that it's been ignored by a mainstream media which he accuses of liberal bias.
So it might be helpful for some wavering voters to be reminded that Barack Obama's mother and grandmother were white, and came from the Midwest state of Kansas.
Partly for that reason, Barack Obama has referred to his grand-mother in two of his most important speeches of the year - his acceptance speech in Denver and his widely-praised "race speech" in Philadelphia, as he grappled with his "pastor problem", the fiery speeches of Jeremiah Wright.
After saying that his grandmother admitted to sometimes being afraid of black men, and uttering the occasional racial stereotype, he noted: "I can no more disown him [Jeremiah Wright] than I can my white grandmother."
In both speeches, he cited the life of his grandmother in a way which helped neutralise the race question.
In his heartfelt statement of condolence, John McCain has shown, once again, his decency and honour. But, again, it's hard to see that influencing many votes at this late stage.
Were this a closer election, we might be speculating about the possibility of a sympathy vote. But the polls suggest a commanding lead for Mr Obama, and so the impact is likely to be negligible.