"I am less familiar with some of these blue-collar voters than [Clinton]. . . . They are less familiar with me than they are with her, and so we probably have to work a little bit harder," Obama said on "Fox News Sunday."

He added, "I've got to be more present. I've got to be knocking on more doors. I've got to be hitting more events."

Howard Wolfson, a top aide to Clinton, said that after Obama's losses among working-class voters in Pennsylvania and Ohio, "I think Democrats do have questions about whether or not he is going to be able to reach out and successfully win over the kind of blue-collar voters that Democrats need to win in order to take the White House back in November."

He said on CBS's "Face the Nation" that Clinton is "somebody who can appeal to working people, people who have real concerns about this economy."

Obama expressed confidence that working- class voters would "vote for me" in a general election. He said his defeat among those voters "shouldn't come as a huge surprise."

Obama acknowledged that some voters were "legitimately offended by some of the comments" made by his former pastor, the Rev. Jeremiah A. Wright Jr., about the country. "The fact he's my former pastor I think makes it a legitimate political issue," Obama said.

But Obama said he goes "to church not to worship the pastor, [but] to worship God. And that ministry, the church family that's been built there, does outstanding work, has been, I think, applauded for its outreach to the poor."