PHILADELPHIA -- Sen. Hillary Rodham Clinton and Sen. Barack Obama wrestled Friday over who was tougher, with Clinton mocking Obama after he earlier complained about his treatment at Wednesday's Democratic debate. Obama ended Friday with a massive rally near Independence Hall.

Clinton brought up the debate at the start of a packed rally at Radnor High School in a posh suburb and alluded to Obama's gripes.

Borrowing President Harry Truman's famous quip, Clinton said, "I'm with Harry Truman on this. 'If you can't stand the heat, get out of the kitchen.' And, just speaking for myself, I'm very comfortable in the kitchen. So as the heat goes up, that's OK with me because we've got a lot of tough problems."

With Tuesday's Pennsylvania primary looming, Obama and Clinton stumped in the Keystone State, with Clinton then heading to North Carolina (voting May 6) for a forum with poet Maya Angelou.

Obama topped off Friday with an outdoor rally in the park adjacent to Independence Hall, drawing about 35,000 people. The Associated Press said it was the largest crowd of his campaign, even larger than the 30,000 people who came to see him and Oprah Winfrey in December in Columbia, S.C.

Friday's rally was in the park adjacent to Independence Hall. Obama alluded to the location in his speech.

"In four days, you get the chance to help bring about the change that we need right now, Philadelphia. Here in the city and the state that gave birth to our democracy, we can declare our independence from the politics that has shut us out and let us down, and told us to settle," he said.

After Clinton started on Obama over who can take the heat, the Obama rapid-response team jumped all over it. Obama spokesman Bill Burton shot out e-mails with a reminder that it was Clinton a while back who was grumbling about getting the first question at debates and harder ones at that.

"Considering the fact that Sen. Clinton sat on stage at the last debate and complained to all of America that she always gets the first question, her blatant hypocrisy here is stunning," Burton said.

Though Obama had complained Thursday about his treatment at the debates, he kept his criticism focused Friday on presumptive GOP nominee John McCain.

"John McCain yesterday said that during George W. Bush's tenure, the economy actually made great progress -- that's his quote," Obama said to his laughing fans in Williamsport, Pa. "Keep in mind, this is a guy that calls me 'out of touch.' This is the first time since World War II that average family incomes went down during an economic expansion."

Clinton picked up the backing of three superdelegates Friday. Obama also was endorsed by former Clinton Labor Secretary Robert Reich and former Senators Sam Nunn of Georgia and David Boren of Oklahoma -- they're not superdelegates, but their support could influence remaining uncommitted superdelegates to go for him.

By Lynn Sweet and Abdon Pallasch, Chicago Sun-Times, April 19, 2008