On Campaign Bus, Obama Opens Up About Challengers

Obama also said he stacks up favorably against Edwards when their earlier records are compared. "Let me put it this way," he said. "If John wants to make the comparison between the work I did as a community organizer -- or as a civil rights attorney or as a state senator taking on special interests -- to him working as a trial lawyer making millions of dollars, I'm happy to have that discussion."

Obama reiterated support for the controversial idea of allowing illegal immigrants to apply for driver's licenses, the issue that created an uproar in the Democratic debate in Philadelphia a week ago. Clinton's halting answer to a related question provided her opponents an opportunity to attack her for refusing to state clearly where she stands on volatile issues.

Obama backed a similar measure as an Illinois state senator and said Thursday, "I would not overrule a state that has decided for public safety purposes that this is the best way to do it."

Obama faced repeated questions about illegal immigration from his Democratic audiences this week and acknowledged that Republicans will make the issue a central part of their campaign.

"My estimation is the Republicans will run on two issues, and two issues only: terrorism and immigration," he said, adding: "There's no doubt there will be attempts made to hit whoever the Democratic nominee is on this issue. And we have to stand our ground and not be defensive."

On Social Security, Obama had previously said that everything would be on the table for discussion as part of negotiations to secure the system's future solvency, including raising the retirement age and reducing benefits. Now he says he prefers raising the cap on the portion of a worker's wages subject to payroll taxes.

"When I said all things are on the table . . . that doesn't mean I don't have clear opinions about how I think we should best proceed," Obama said.

In contrast to Clinton, Obama said he would offer his own Social Security proposal as president and that he would hope to have gained a mandate for changing the system through the campaign.

As the interview drew to a close, Obama expressed great confidence in his ability to change the political environment -- and the political map in America. Asked what red states he could win, he named Virginia and added provocatively, "I think I can put Mississippi in play" because of the high percentage of African Americans in the state, despite the fact that it has been one of the most reliably Republican states in the nation."