Barack Obama will suspend his campaigning for more than 36 hours this week to visit his grandmother Madelyn Dunham, who is gravely ill in Hawaii.

Dunham, 85, all but raised Obama during his teenage years in Hawaii, and he has spoken of her often on the campaign trail. A campaign spokesman, Robert Gibbs, declined to specify the nature of her illness, other than to say it was quite serious. Dunham lives in Honolulu.

“I think everyone understands that the decision that Senator Obama is making to go to Hawaii underscores the seriousness of the situation,” Gibbs said. “As he has said, she poured everything she had into him.”

The Obama campaign has canceled scheduled appearances by Obama in Des Moines and Madison, Wisconsin. But the senator will make an unexpected stop in Indianapolis on Thursday, Gibbs said, since that aligns more easily with his plan to depart for Hawaii.

Obama will fly to Hawaii on Thursday afternoon, and likely depart back to the mainland Friday evening. Gibbs said he is expected to return to the campaign trail on Saturday.

To leave the trail at this juncture, when the bell lap is upon both Obama and his Republican rival John McCain carries an element of risk. Obama is running ahead in every national poll, but his lead in some recent polls is not large.

But Obama has little family left. His father and mother are dead, along with his grandfather, Stanley Dunham. His grandmother raised him for many years, while his mother lived in Indonesia.