"The people who say this haven't apparently been listening to me," the likely Democratic presidential nominee said in response to a question at a town-hall style event.

Obama blamed criticism from "my friends on the left" and "some of the media" in part on cynicism that ascribes political motives for every move candidates make. "You're not going to agree with me on 100 percent of what I think, but don't assume that if I don't agree with you on something that it must be because I'm doing that politically," he said. "I may just disagree with you."

The Illinois senator was responding to a question from a self-described "reformed Republican" who said he worked for Democrat Bobby Kennedy four decades ago and thanked Obama for restoring "that faith."

"You had an interesting week of being accused of flip-flopping, which is mostly nonsense," the man said. He then asked Obama to restate his Iraq position, and Obama used the opportunity to dispel the idea he had generally changed his stances.

Since wrapping up the Democratic nomination last month, Obama has voiced positions that break with the Democratic Party's left and seem to shade his own past positions on a range of subjects. He's drawn criticism from some liberal Democrats who question his loyalty and from Republicans who accuse him of flip-flopping.

His remarks aside, Obama is clearly competing for the center of the electorate. Originally best known as an anti-Iraq war candidate, his general election commercials appear nonpartisan and make an obvious play for voters across the political spectrum by focusing on family values and patriotism as well as "welfare to work" and lower taxes.

Over the past few weeks, he angered liberals by supporting compromise electronic surveillance rules for the government's wiretapping program even though the bill provided immunity that he opposed last year for telecommunications companies that conducted warrantless eavesdropping. When the Supreme Court overturned the District of Columbia's gun ban, he said he favors both an individual's right to bear firearms and a government's right to regulate them.

And, he broke with death penalty opponents when he disagreed with the Supreme Court's decision outlawing executions of people who rape children.