Barack Obama swept to victory in the North Carolina primary on Tuesday but fell behind Hillary Rodham Clinton in Indiana, the last big-delegate prizes left in their long race for the Democratic presidential nomination.
Obama's win mirrored earlier triumphs in Southern states with large black populations, Georgia, Alabama, Louisiana and South Carolina among them.
The Associated Press made its North Carolina call based on surveys of voters as they left the polls.
That made Indiana a virtual must-win Midwestern state for the former first lady, who was hoping to counter Obama's persistent delegate advantage with a strong run through the late primaries.
Returns from 99 percent of the Indiana precincts showed Clinton with 51 percent of the vote to 49 percent for Obama.
The economy was the top issue by far in both states, according to interviews with voters as they left their polling places.
Indiana exit polls charted a racial divide that has become familiar in a long, historic campaign pitting a black man against a white woman.
Obama was gaining more than 90 percent of the black vote in Indiana, while Clinton was winning an estimated 61 percent of the white vote there, running ahead of her rival among white men as well as women.
She also had 51 percent of independents' votes, to 49 for her rival, a statistical tie, and was winning among Democrats, 53-47.
In North Carolina, Clinton won 60 percent of the white vote, but Obama claimed support from roughly 90 percent of the blacks who cast ballots.
The impact of a long-running controversy over Obama's former pastor, the Rev. Jeremiah Wright, was difficult to measure.
In North Carolina, six in 10 voters who said Wright's incendiary comments affected their votes sided with Clinton. A somewhat larger percentage of voters who said the pastor's remarks did not matter supported Obama.
The effect of Clinton's call for a summertime suspension of the federal gasoline tax — which dominated the final days of the two primaries — was impossible to judge.
The questionnaire used to learn about voter motivation did not include any questions about the gasoline tax.
In Indiana, about one in five voters said they were independents, an additional one in 10 said Republican.
Only Democrats and unaffiliated voters were permitted to vote in North Carolina.
Voting in Indiana was carried out under a state law, recently upheld by the Supreme Court, that requires voters to produce a valid photo ID. About a dozen nuns in their 80s and 90s at St. Mary's Convent in South Bend were denied ballots because they lacked the necessary identification.
Obama began the day with 1,745.5 delegates, to 1,608 for Clinton, out of 2,025 needed for the nomination.
Both races were dominated in the final days by Clinton's call for a summertime suspension of the federal gasoline tax, an issue that she created after scoring a victory in the Pennsylvania primary two weeks ago.
Obama ridiculed the proposal as a stunt that would cost jobs, not the break for consumers she claimed. The two rivals dug in, devoting personal campaign time and television commercials to the issue.
Indiana had 72 delegates at stake, and Clinton projected confidence about the results by arranging a primary-night appearance in Indianapolis.
North Carolina had 115 delegates at stake, and Obama countered with a rally in Raleigh.
Obama leads Clinton in delegates won in primaries and caucuses. Despite his defeat two weeks ago, he has steadily whittled away at her advantage in superdelegates in the past two weeks and trails 269.5 to 255.
Clinton saved her candidacy with her win in Pennsylvania, and she campaigned aggressively in Indiana in hopes of denying Obama a victory next door to his home state of Illinois. Indiana is home to large numbers of blue-collar workers who have been attracted to the former first lady, and she sought to use her call for a federal gas tax holiday to draw them and other economically pinched voters closer.
Inevitably, the issue quickly took on larger dimensions.
Obama said it symbolized a candidacy consisting of "phony ideas, calculated to win elections instead of actually solving problems."
Clinton retorted, "Instead of attacking the problem, he's attacking my solutions," and ran an ad in the campaign's final hours that said she "gets it."
To a large extent, the gasoline tax eclipsed the controversy surrounding Obama's former pastor. After saying several weeks earlier he could not disown the Rev. Jeremiah Wright for his fiery sermons, Obama did precisely that when the minister embarked on a media tour.
At a news conference in North Carolina last week, Obama equated Wright's comments with "giving comfort to those who prey on hate."
The balance of the primary schedule includes West Virginia, with 28 delegates on May 13; Oregon with 52 and Kentucky with 51 a week later; Puerto Rico with 55 delegates on June 1, and Montana with 16 and South Dakota with 15 on June 3.
Sen. John McCain of Arizona, the Republican nomination already in hand, campaigned in North Carolina and assailed Obama for his vote against confirmation of Chief Justice John Roberts.
"Senator Obama in particular likes to talk up his background as a lecturer on law, and also as someone who can work across the aisle to get things done," McCain said. "But ... he went right along with the partisan crowd, and was among the 22 senators to vote against this highly qualified nominee."
Clinton also voted against Roberts, but McCain, as is often the case, focused his remarks on Obama.
Obama's campaign responded that the Republican would pick judges who represent a threat to abortion rights and to McCain's own legislation to limit the role of money in political campaigns.