Of course, there's the little matter of a Pennsylvania primary on April 22, and Clinton's double-digit lead in recent state polls.
The extended presidential nomination contest has resulted in an odd political triangle, with each candidate taking alternate turns criticizing one or both of their competitors.
"He's on a biography tour right now," Obama said of McCain. "Most of us know his biography, and it's worthy of our admiration. My argument with John McCain is not with his biography, it's with his policies."
Obama argued that McCain would merely be another four years of President Bush on economic and military policies. McCain has criticized Obama as being inexperienced on national security, and the Illinois senator answered back.
"Meanwhile Senator McCain has been saying I don't understand national security, but he's the one who wants to keep tens of thousands of United States troops in Iraq for as long as 100 years," Obama said.
The McCain and Obama camps have been feuding for days over remarks McCain recently made when he said the U.S. could end up having a long-term military presence in Iraq, similar to the more than 50-year presence of U.S. soldiers in Germany and South Korea.
"One hundred years in a country that had nothing to do with 9/11 may make sense to George Bush and John McCain but it is the wrong thing to do. It is not right for our national security. It is not right for our economy," Obama said to applause at a town hall.
McCain spokesman Tucker Bounds said Obama's remarks show his "complete lack of preparedness to be commander in chief."
"His attempt to paint McCain's position as something else is nothing but the disingenuous, old-style politics that he claims to reject," Bounds said.
Though the primary contest has heightened tensions among Democrats fearful it will hurt their chances of winning the general election in November, Obama told the crowd not to worry.
"I don't buy this whole thing that people are super-divided," he said in response to a question. "We are going to come together and focus on the fact that John McCain wants to continue the war in Iraq, I want to end it, John McCain wants to continue George Bush's economic policies."
For all his complaints about McCain, Obama also talked tough on international trade issues -- a sensitive subject in a state with plenty of blue-collar Democratic votes to be won.
An Iraq war veteran asked the senator's opinion of a recent decision by the Pentagon to award a $35 billion Air Force tanker contract to a consortium led by Airbus, located in Europe, over a bid led by U.S.-based Boeing.
Obama said he had concerns about the deal but an investigation was warranted to find out more.
"I don't mind the Pentagon procuring from other countries but when you've got such an enormous contract for such a vital piece of our U.S. military arsenal, it strikes me that we should have identified a U.S. company that could do it," he said, though he added that he might conclude the decision was justified if it turns out Airbus' bid was 10-15 percent better than Boeing's.
McCain has faced questions about the contract because some of his current advisers lobbied last year for the European Aeronautic Defence and Space Co., the parent company of plane maker Airbus. EADS and its U.S. partner Northrop Grumman Corp. beat Boeing Co. for the lucrative aerial refueling contract.
McCain has said his inquiries into the contract were designed to ensure evenhanded bidding and denied they were motivated by lobbyists who are close advisers to his presidential campaign.
Obama cautioned that just protecting jobs won't be enough, that the government must do more to nurture workers and businesses that can thrive in the global economy.
"Those who want to draw a moat around America, it's not going to work, with the internet with technology with automation we've got to compete," he said.