The Illinois Democrat said he could no longer stand by the statements he made after his 2004 election and earlier this year that he would serve a full six-year term in Congress. He said he would not make a decision until after the Nov. 7 elections.
"That was how I was thinking at that time," said Obama, when asked on NBC's "Meet the Press" about his previous statements.
"Given the response I've been getting the last several months, I have thought about the possibility" although not with any seriousness or depth, he said. "My focus is on '06. ... After November 7, I'll sit down and consider it. If at some point I change my mind, I will make a public announcement, and everybody will be able to go at me."
If every presidential candidate has to have a great story to tell, Barak Obama's life certainly qualifies, reports CBS News correspondent Gloria Borger.
He was the first African-American to edit the Harvard Law Review. By 1996 he was in the state senate, then was elected to the U.S. Senate in 2004. Now, after just two years on the national stage, he's a certified political phenomenon.
Nevertheless, Obama was largely unknown outside Illinois until he burst onto the national scene with a widely acclaimed address at the 2004 Democratic National Convention.
In recent weeks, his political stock has been rising as a potentially viable centrist candidate for president in 2008 after former Virginia Gov. Mark Warner announced earlier this month that he was bowing out of the race.
In a recent issue of Time magazine, Obama's face fills the cover next to the headline, "Why Barack Obama Could Be The Next President." He is currently on a tour promoting his latest book, "The Audacity of Hope: Thoughts on Reclaiming the American Dream."
On Sunday, Obama dismissed notions that he might not be ready to run for president because of his limited experience in national politics. He agreed the job requires a "certain soberness and seriousness" and "can't be something you pursue on the basis of vanity and ambition."
"I'm not sure anyone is ready to be president before they're president," Obama said. "I trust the judgment of the American people.
"We have a long and vigorous process. Should I decide to run, if I ever decide to, I'll be confident that I'll be run through the paces pretty well," Obama said.
But here's something else to think about, adds Borger. He's 98th on the Senate seniority list, and without any serious national security credentials. So the question remains: Is it really time for Obama to run, or is it too far, too fast?