Obama also had to defend himself in a recent controversy over inflammatory comments by his pastor, the Rev. Jeremiah Wright.
"I specifically said that these comments were objectionable. They're not comments that I believe in. And I disassociated myself with them," he said.
PENNSYLVANIA SHOWDOWN
The controversies have roiled the Democratic presidential race during a seven-week lull between the last round of major contests in Ohio and Texas on March 4 and next week's showdown in Pennsylvania.
Clinton has a dwindling lead over Obama in state polls, and needs a big win to try to close the gap on the Illinois senator in popular votes and pledged delegates to the nominating convention.
With 10 contests remaining, Obama has a nearly unassailable lead in pledged delegates, but neither candidate is likely to gain enough delegates to win without help from nearly 800 Democratic Party officials and insiders who are free to back any candidate.
When pressed whether she thought Obama could win in November and beat back attacks from Republicans, Clinton said: "Yes, yes, yes. Now I think that I can do a better job. Obviously that's why I'm here."
"I believe I am the better and stronger candidate than Senator McCain and I can go toe to toe with him on national security," she said.
Both candidates said they would move forcefully to ensure Iran does not acquire nuclear weapons, and would make it clear that an attack on Israel would prompt U.S. retaliation.
"I will do whatever is required to prevent the Iranians from obtaining nuclear weapons," Obama said.
The two candidates also agreed they would not raise taxes on Americans making less than $200,000 a year.
Obama was asked by a voter via video why he did not wear the American flag in his lapel.
"I have never said that I don't wear flag pins or refuse to wear flag pins. This is the kind of manufactured issue that our politics has become obsessed with and, once again, distracts us," he said.
