Philadelphia, April 17: A fatigued and hesitant Barack Obama appeared badly rattled when peppered with almost relentlessly hostile questions combined with strident attacks from his rival Hillary Clinton during a televised debate this morning.

Obama, who holds a clear national opinion poll lead and seemed to have weathered recent crises before Tuesday’s crucial Pennsylvania primary, gave what even his allies said was perhaps his poorest performance of the 21 Democratic debates.

He was taken aback by the succession of questions about his recent comments that voters were clinging to religion and guns because they were “bitter”, his association with a former member of the 1960s terrorist Weather Underground group, his controversial pastor the Reverend Jeremiah Wright and even why he did not wear a flag lapel pin.

Whether Clinton will benefit from the debate, however, remains to be seen. Her “high negatives” and low marks for trustworthiness in polls mean that every time she goes on the offensive she risks alienating undecided voters and reminding them of the partisan battles of the 1990s.

The more uncomfortable Obama seemed in the Philadelphia debate, the more pointed Clinton’s jabs became.

“For Pastor Wright to have given his first sermon after 9/11 and to have blamed the US for the attack, which happened in my city of New York, would have been just intolerable for me,” she said, noting that Obama had not left Rev Wright’s church.

She also blasted Obama for sitting on the board of a Chicago philanthropic group with links to William Ayers, a former member of the Weather Underground. In comments published, coincidentally, on September 11, 2001, Ayers was unrepentant about bombing the Pentagon.

Clinton said: “If I’m not mistaken, that relationship with Ayers on this board continued after 9/11 and after his reported comments, which were deeply hurtful to people in New York and, I would hope, to every American, because they were published on 9/11, and he said that he was just sorry they hadn’t done more."

Obama protested: “The problem is that that’s the kind of politics that we’ve been accustomed to. And I think Senator Clinton learned the wrong lesson from it because she’s adopting the same tactics.

“What the American people want are not distractions. They want to figure out, how are we going to actually deliver on health care? How are we going to deliver better jobs for people?” Afterwards, the Illinois senator’s aides were livid, complaining that the ABC News debate was unfair and an example of “old politics” designed to tear a candidate down.

“I’ve never seen anything quite like it,” said David Axelrod, Obama’s chief strategist. “People around Pennsylvania were probably asking what the heck is going on.” He added: “I would think she [Clinton] enjoyed it a lot. It’s easy when you can sit back and the moderators direct all their questions at one candidate.”

But Clinton also came under pressure at times. She came close to saying that she had lied by embellishing her account of a 1996 visit to Bosnia by saying she had landed under sniper fire. “I’m very sorry that I said it,” she said. “And I have said that, you know, it just didn’t jive with what I had written about and knew to be the truth.”