ORLANDO, Fla. -- Hours after speaking in front of some 60,000 people in Orlando, Sen. Barack Obama canceled campaign events scheduled for later this week to fly to Hawaii to visit his gravely ill 85-year-old grandmother, a campaign spokesman said.

Robert Gibbs told reporters aboard Obama's plane that Madelyn Payne Dunham, who helped raise Obama, was released from the hospital late last week. But he said her health had deteriorated "to the point where her situation is very serious."

Events originally planned for Madison, Wis., and Des Moines, Iowa, on Thursday will be replaced with 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.

"Sen. 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." Dunham turns 86 on Sunday.

It could be a momentous one in his bid for the White House against Republican John McCain, 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.

Obama last visited Hawaii in August, when he spent a week on vacation after he had clinched the Democratic presidential nomination.

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