Flying from Texas back home to Chicago on Wednesday morning, Mr. Obama delivered the message that he intended to counterpunch forcefully.  His campaign aides on Wednesday urged Mrs. Clinton to release her tax returns from 2006, as well as her papers from her years as first lady, which Mr. Obama’s chief strategist, David Axelrod, described as “secreted in the Clinton library.”  “She’s made the argument that she’s thoroughly vetted, in contrast to me,” Mr. Obama said to reporters aboard his campaign plane. “I think it’s important to examine that argument.”  Over the last year, though, Mr. Obama has struggled to deliver that examination. He picks up the cudgel, and then sets it down. The problem is that Mr. Obama has built a campaign persona as the man of hope, a young candidate with oratorical skills who promises to build bridges across the ideological divide.  If he indulges his inner Chicago pol, formed in a city where politics is conducted with crowbars, he risks taking the shine off. But his advisers say he has little choice.  Mr. Obama took aim on Wednesday at Mrs. Clinton’s claim that she is a seasoned hand in foreign policy. “What exactly is this foreign experience that she’s claiming?” he said. “I know she talks about visiting 80 countries. It is not clear. Was she negotiating treaties or agreements or was she handling crises during this period of time?  “My sense is the answer’s no.”  Mr. Obama, finally, has tactical worries of his own. He won in states like Missouri by running up large margins in cities and suburbs. But in Ohio, he appeared outorganized.  Gov. Ted Strickland, who endorsed Mrs. Clinton, advised her to encircle the cities. Mr. Strickland led her deep into his base in the hills of Appalachia in southern Ohio; Bill Clinton also passed through the region when he was president. Mrs. Clinton ran up big margins in those rural counties.  Mr. Obama retains significant advantages, including his lead among pledged delegates and a record-setting fund-raising operation. And he bridled at questions on Wednesday about his difficulties attracting working-class and middle-class support, noting his progress in that regard.  “I don’t buy into this demographic argument,” Mr. Obama said. “In Missouri, Wisconsin, Virginia and many of these states, we’ve won the white vote and the blue-collar voters. I think it is very important not to somehow focus on a handful of states because the Clintons say that those states are important and the other states are unimportant.”  His advisers pointed out that the Clinton campaign had built up 20-point leads in the polls in Ohio and Texas just two weeks ago and that Mrs. Clinton’s tough tactics and negative advertisements forced the Obama campaign upon the shoals.  But Mr. Obama is hardly a by-the-bootstraps insurgent. He had a decided financial advantage in both states, outspending the Clinton campaign more than two to one, and he could count on the support of powerful unions and the endorsement of a string of big-city mayors.  “I’ll tell you what I would do now,” said Mayor Michael B. Coleman of Columbus, Ohio, who had endorsed Mr. Obama. “I would start to draw contrasts with her. I don’t think Obama has focused on that, and there are opportunities to be explored there.”  Mr. Obama seems likely to take a tougher stance toward Mrs. Clinton, if only because he saw how well such tactics worked against him. When the Clinton campaign attacked on multiple fronts last week, he sometimes sounded defensive, occasionally talking at his audiences rather than with them.  “There’s no magic bullet that hurt him; it was a series of bullets,” said Hank Sheinkopf, a Democratic consultant. “She reduced his charisma and forced voters back to reality.”  For now, Mr. Obama and his advisers are huddled in Chicago, plotting strategy.  Asked on the plane whether he and Mrs. Clinton might make a good ticket, he smiled. “It’s very premature,” he said, “to start talking about a joint ticket.”  A version of this article appears in print on , on Page A1 of the New York edition with the headline: Lesson of Defeat: Obama Comes Out Punching. Order Reprints| Today's Paper|Subscribe
After appearing nearly invincible last week, Barack Obama now faces questions about whether he can win states vital to a Democratic victory in November.