Both Sen. Hillary Rodham Clinton, D-N.Y., and her husband, former President Clinton, have criticized Obama for his lack of political experience.
Obama said he understands their argument.
"They want to make the argument that Senator Clinton is just an extension of the Bill Clinton presidency," Obama said in an interview with The Associated Press. "They've been the dominant political family in the Democratic Party for the last 20 years now. So it's not surprising that they want to focus on their longevity.
But, Obama said: "My belief is that the American people are looking for a fundamental break from the way we've been doing business."
Obama said his opposition to the Iraq war before combat began shows his experience. Clinton voted to authorize military action in Iraq.
"On the single most important foreign policy issue of our time, I got it right," Obama said.
This week marks the fifth anniversary of a speech Obama gave in 2002 opposing the Iraq war, and he'll spend the week revisiting that address and discussing the foreign policy challenges he says it has created.
Obama's campaign on Sunday also announced that it had surpassed 350,000 donors for the year, a significant feat at this stage in any campaign. In a letter to supporters, Obama campaign manager David Plouffe said the donors represented more than 500,000 donations. At midyear, the campaign had reported getting contributions from more than 250,000 individual donors, meaning that about 100,000 new donors contributed to him during the past three months.
The campaign did not announce how much money it had raised during the last quarter. The number of new donors is less than what he attracted between the beginning of April and the end of June, but it would match the number of donors to his campaign in the first three months of the year, when he raised $25.7 million. By midyear, Obama had raised $58.5 million, making him the top fundraiser in the presidential race.
Obama attended religious services at Baptist churches Sunday, showing little apparent concern about the third-quarter fundraising deadline. He raised more than $58 million in the first six months of the year.
"We've done a remarkable job fundraising," Obama said, adding his campaign has more than 300,000 donors. "We have more donors giving $200 or less than all the other Democratic candidates combined."
He refused to say how much he had raised in the quarter ending Sunday night.
Obama faced questions earlier this week after his wife, Michelle, told Iowans that her husband had to win the state's caucuses. He said Sunday he will concentrate on Iowa, New Hampshire, Nevada and South Carolina.
"We've got four early states and the premise of our campaign is we need to do well in all of those early states because we've been in the national spotlight for the shortest amount of time," Obama said. "The early states provide a wonderful launching pad for that. And so when we're in Iowa, we say to Iowans, 'You know, we really need you.' And when I'm in South Carolina, I tell South Carolinians I really need them."
Obama found stark contrasts at the two churches - one with a predominantly black congregation, the other mostly white.
At West Columbia's Brookland Baptist, one of the largest black churches in the Columbia area, worshippers stood, clapped and cheered as Obama slipped in through a side door. The service included references to his political aspirations and prayers for his safety, and he swayed to the music with the rest of the congregation.
A couple of miles away, Obama was barely noticed when he slipped in to the mostly white First Baptist Church. Traveling minister Joe White carried a pole on his shoulder into church, and swung an ax to make a cross and nail it together.
"That's some serious work he was doing," Obama said afterward.