Robert Gibbs told reporters Monday that Obama's grandmother, Madelyn Payne Dunham, who helped raise him, was released from the hospital late last week. But he said her health had deteriorated "to the point where her situation is very serious."
"It's not preferable for a campaign to have their candidate off the trail even for a short period of time in the final days of a race," said CBSNews.com senior political editor Vaughn Ververs. "But voters will certainly understand, even appreciate, Obama's decision and it should have little to no impact on the campaign itself."
Events originally planned for Madison, Wis., and Des Moines, Iowa, on Thursday will be replaced by one in Indianapolis before he makes the long flight to Hawaii. On Friday, Obama's wife, Michelle, will sub for Obama at rallies in Akron and Columbus, in Ohio, said campaign spokeswoman Jen Psaki. Obama was expected to resume campaigning on Saturday, at an undecided location in the West, she said.
"Senator Obama's grandmother, Madelyn Dunham, has always been one of the most important people in his life, along with his mother and his grandfather," Gibbs said. "Recently his grandmother has become ill and in the last few weeks her health has deteriorated to the point where her situation is very serious. It is for that reason that Sen. Obama has decided to change his schedule on Thursday and Friday so that he can see her and spend some time with her."
Citing the family's desire for privacy, Gibbs would not discuss the nature of Dunham's illness. It seemed likely that she was close to death, as Gibbs said that "everyone understands the decision that Sen. Obama is making."
It could be a momentous one for his bid for the White House against Republican , with Election Day just two weeks away on Nov. 4.
In a campaign ad this year, Obama described his Dunham as the daughter of a Midwest oil company clerk who "taught me values straight from the Kansas heartland" - things like "accountability and self-reliance. Love of country. Working hard without making excuses. Treating your neighbor as you'd like to be treated."
She's also the "white grandmother" he referred to in a speech on race.
Earlier this year, Obama talked to CBS News anchor Katie Couric about her.
"She's been the rock of my family. She worked very hard all her life, and made a lot of sacrifices on my behalf."
Obama also recognized Dunham when he accepted the Democratic presidential nomination at the party's convention in Denver.
"She's the one who taught me about hard work. She's the one who put off buying a new car or a new dress for herself so that I could have a better life. She poured everything she had into me. And although she can no longer travel, I know that she's watching tonight, and that tonight is her night as well," he said.
Obama last visited Hawaii in August, when he spent a week on vacation after clinching the Democratic presidential nomination.