After Clinton's questioning, her political rival, Barack Obama, took the stage to answer his own set of hard questions.
Obama's first question was about his controversial remark last week that decades of lost jobs and unfulfilled promises from Washington have left some Pennsylvanians "bitter". He said they were "clinging to guns or religion or antipathy to people who aren't like them or anti-immigrant sentiment or anti-trade sentiment as way to explain their frustrations," according to CNN.
At Sunday's forum, he sought to clarify his comment saying that "religion is a bulwark, a foundation when other things aren't going well". He also reaffirmed his faith saying, "I am a devout Christian," and said he wasn't "demeaning" a faith he embraced.
"Nobody in a presidential campaign on the Democratic side in recent memory has done more to reach out to the church and talk about, what are our obligations religiously, in terms of doing good works, and how does that inform our politics?" Obama defended himself.
After a few tough political questions, Obama faced some tough theological questions, including if he believes God intervenes in history and rewards and punishes nations.
Obama responded that he believes that God does intervene, but the concept is "too mysterious" for him to grasp. He said all he can do is try his best to be an instrument to do God's will and apply what he believes is the core value - to be his brothers' and sisters' keeper - then he is moving God's agenda forward, even though he doesn't know what the "master plan" is.
On the abortion issue, Obama believes "absolutely" that pro-choice and pro-life supporters can find common ground. He said pro-choice people must acknowledge there is a moral ground in the debate and that it is a heart-wrenching choice. Secondly, both sides must admit there can be people of "goodwill" that exist on both sides of the issue on abortion.
"If we can acknowledge that much we can agree we can do everything to avoid someone facing that choice," he said. But he stated that ultimately he believes it is the woman's choice in consultation with her doctor and family to make the decision if she should keep a child.
The Illinois senator supports a comprehensive approach to the abortion problem that includes abstinence education, medical care improvement, contraception and adoption.
Obama also answered a question about the creation story in the Book of Genesis. He said he understands there is a debate about whether the universe was created in six days literally or not. The man running to be the first black US president said he does not believe that the universe was created in 24 hour day periods although he believes the Bible's creation story is "fundamentally" true. He also added that he believes in evolution and that it is not incompatible with the Christian faith. Rather, as he knows more about science it strengthens his faith.
Toward the end, Obama, who has been accused of being a secret-Muslim, was asked about his exposure to Islam as a child growing up in Indonesia - the world's most populous Muslim country.
He said that he first attended a Catholic school in Indonesia before going to a public school. His experience in Indonesia exposed him to tolerant Muslims living under a secular constitution where some Muslim women do not even wear the traditional head covering. As a result of his experience, he says most Muslims are goodwilled, trying to raise their kids the best they can.
Commentators after the faith forum noted how far the Democrats have gone in addressing religion and politics, which had formerly been monopolised by the Republican Party. They also observed that evangelicals have changed and are broadening their issues beyond abortion and traditional marriage to include Darfur, torture, HIV and Aids, climate change and poverty.
The presidential candidates forum on faith took place nine days before the Pennsylvania primary. Senator John McCain, the presumptive Republican nominee, was invited to participate but declined.
