"You can call me Hillrod," said Clinton of her WWE persona, and Obama asked the audience, "Do you smell what Barack is cooking?"
While Clinton held a late-night rally in Philadelphia, Obama laughed through his appearance on Jon Stewart's "The Daily Show."
But there was a different tone this morning, as both candidates appeared on "Good Morning America" to discuss a nuclear Iran and their expectations for the outcome of today's primary vote.
In an interview with ABC News' Chris Cuomo, Clinton expressed her toughest stance yet on Iran's nuclear ambitions and the potential threat the country poses to American allies.
"If Iran were to launch a nuclear attack on Israel what would our response be?" Clinton said. "I want the Iranians to know that if I'm the president, we will attack Iran. That's what we will do. There is no safe haven."
"Whatever stage of development they might be in their nuclear weapons program in the next 10 years during which they may foolishly consider launching an attack on Israel, we would be able to totally obliterate them," Clinton said.
Clinton's tough talk on Iran came a day after she launched a TV ad in Pennsylvania that included the ominous face of al Qaeda leader Osama bin Laden. Clinton introduced bin Laden into the campaign along with the narrator's voice warning, "It's the toughest job in the world. You need to be ready for anything."
When asked how he would respond to a nuclear attack by Iran, Obama told ABC News' Robin Roberts that he would do everything he could to prevent the country from having weapons in the first place.
"I was absolutely clear about the fact that if Iran used nuclear weapons on Israel, or any of our allies, we would respond forcefully and swiftly," said Obama.
"But, in some ways, this hypothetical presupposes a failure to begin with," said Obama. "We shouldn't allow Iran to have nuclear weapons, period."
"I have consistently said that I will do everything in my power to prevent them from having it and I have not ruled out military force as an option," he said.
Obama suggested that Clinton's use of terms such as "obliterate" in reference to Iran are ineffective "saber rattling."
"Talk using words like obliterate doesn't actually produce good results," said Obama. "I think the Iranians can be confident that I will respond forcefully, and it will be completely unacceptable if they attacked Israel, or any other of our allies in the region, with conventional weapons or nuclear weapons."
Clinton: 'I Have to Win'
When asked what the measure is by which she needs to win the Pennsylvania primary, Clinton said, "Well, I have to win. I believe that's my task."
"I know very well that I'm in a real fight here," Clinton said about her tight race against Obama. "Every time I turn around there are posters at bus stops and train trips and he's got an enormous cash advantage."
Clinton told Cuomo that Pennsylvania is a must-win state for any Democrat who wants to win the White House in November.
"I think there's a big burden on Sen. Obama tomorrow to prove that he can win a big state, because he hasn't really up until now," she said.
Obama appeared optimistic about his chances in Pennsylvania.
"I think all we do is just work as hard as we can," said Obama, when asked how he defines success in today's primary.
"Sen. Clinton started off with a big lead here. She had a 20-point lead," he said. "But we feel good about how we've chipped away at that lead."
Obama also took time to go after the GOP candidate John McCain and his recent remark that even McCain would be better than President Bush. But Obama said McCain would still mimic the current administration too much.
"Some of his instincts may be better than President Bush's, but the policies that he's putting forward right now essentially offer a continuation of George Bush's term," said Obama.
When asked whether McCain would be better than Bush, Obama responded, "He might be better in some areas, and he might be worse in others."
"Part of what we have to watch as this campaign unfolds is what is he willing to say to get elected," said Obama.
Clinton, Obama Talk Gas, Experience
With the average price of gas in Pennsylvania hitting $3.49, Obama told ABC News that he would help voters fill their tanks by giving them more money.
"We've got to get some more money in their pockets because we're not going to immediately reduce oil prices on the world stage," said Obama. "But what we can do is provide a middle class tax cut that puts more money in the pockets of families to deal with higher costs."
In a lighter moment, Clinton was asked how voters should differentiate between the plans or "meal" she and Obama are "bringing to the table" for the American people.
"Well, I think I'm a more experienced cook, and I think my meal will be better seasoned," Clinton said laughing.
ABC News' Chris Cuomo, Eloise Harper, Cole Kazdin, and Jay Shaylor contributed to this report.