Trailing in delegates and the popular vote, Clinton has been stepping up the pressure on Obama for more debates before the upcoming primaries, which are crucial to her candidacy.
She also has been reaching out to uncommitted Democratic superdelegates in hopes of capitalizing on her Pennsylvania primary victory.
Clinton's Pennsylvania victory was buoyed by support from working-class and white voters, but Obama dismissed the notion yesterday that race will be a factor in the presidential election.
"Is race still a factor in our society? Yes. I don't think anybody would deny that," he said on "Fox News Sunday."
"Is that going to be the determining factor in a general election? No, because I'm absolutely confident that the American people - what they're looking for is somebody who can solve their problems."
Addressing whether superdelegates should back the candidate with the most pledged delegates and popular vote, Obama said he believed voters will be frustrated if Democratic superdelegates choose to back the trailing candidate. He expressed confidence that he can convince superdelegates that he is more electable.
"I think we should find that person who is going to be best able to not just defeat John McCain, but also lead the country. I happen to think I'm that person," Obama said. "I will make that argument forcefully to the superdelegates prior to the convention."
Superdelegates are party members who are automatically selected to attend the convention and are not bound by the popular vote in their states' primaries and caucuses.
Speaking to reporters in Indiana, Obama declined to set expectations on a margin of victory in that state.
"I think winning is winning - 50 plus 1," Obama said. "Indiana is a very important state, so is North Carolina, we're not taking that for granted. There's no doubt it's close. We feel very strongly that our message of bringing change to Washington is going to resonate in Indiana."
Polls put Obama in the lead in North Carolina, but the race in Indiana is considered too close to call.
Campaigning in Wilmington, N.C., yesterday, Clinton said the assassination attempt President Hamid Karzai of Afghanistan shows that the United States has failed to give proper attention to that country.
