March 6, 2008 -- In reflecting on the results of Tuesday's primaries in Ohio and Texas, Sen. Barack Obama, D-Ill., admitted in an exclusive interview with ABC News that his campaign has made some mistakes and that his task now is to answer the charges being lived at him and to remind voters of why he got into the race.

Watch the video here.

"I think people started saying, 'well, maybe we want this to continue a little bit further.' They want me to earn this thing and not feel as if I'm just sliding into it. And, you know, I think we made some mistakes, as well, which is inevitable during the course of a long campaign," Obama told World News' Anchor Charles Gibson.

Watch the video here and "World News" Thursday at 6:30 pm ET.

"But what we want to do is make sure that, going forward, that people understand why I got into this race, they understand that when I opposed this war in Iraq from the start, or I decided not to take PAC money or federal registered lobbyist money, that that stands in stark contrast to the way business in Washington has typically been done."

Still maintaining a big advantage in delegates and fundraising, the Obama campaign has stepped up its engagement with Sen. Clinton over the past 48 hours since the former first lady's impressive three state victory on Tuesday. And now, Obama signaled he's ready to flip the script, personally.

Asked if his campaign needs to show some toughness greater than it's shown so far, Obama said, "We're going to have to make sure that we're not just letting a bunch of charges go unanswered."

On her taxes, "You know, if Senator Clinton wants, for example, to talk about issues of transparency and vetting, then I think it's important for her to release her tax returns, as I have, and as many presidential candidates in the past have."

On experiences, "I think Senator Clinton, like Senator McCain, believes that life begins when you arrive in Washington. So she discounts all the work that I've done as a community organizer, as a civil rights attorney, as somebody who taught constitutional law, as a state senator, as well as a United States senator. Apparently, to her, that's irrelevant," he said.

"On the other hand, all her experience is relevant, work at the Rose Law Firm or her work as first lady. So that's something, obviously, that we're going to contest," he continued.

Obama wouldn't say whether he favors a re-vote in Michigan and Florida only that the issue should be resolved by the Democratic National Committee.

The outcome in the struggle over what to do with the Democratic contests in Florida and Michigan -- which are not being counted because the states held their contests in violation with party rules -- could become critical in determining the nominee, since neither Obama or Clinton can garner enough delegates to win the nomination in the remaining contests.

As the campaign moves on with contests in Wyoming this weekend and Mississippi next week, Obama hopes to keep to his core message. "I want to spend time talking about the $4,000 tuition credit for every student, every year, in exchange for national service that can make college affordable. I want to talk about middle-class tax cuts for families making less than $75,000 a year. Those are the things that I'm going to continue to push forward."