Louisiana Sen. David Vitter (R) was asked to explain his "serious sin" during a debate with Democratic challenger Charlie Melancon Thursday night.

It was the second debate of the campaign, but the first time Vitter has taken questions from reporters about his infamous confession.

Vitter's telephone number appeared in the phone records of the "D.C. Madam" prostitution ring in 2007. The calls dated from before his run for Senate in 2004. He issued a statement apologizing for committing a "serious sin," but never elaborated.

"Greg, I’ll be honest with you," Vitter said to WAFB television reporter Greg Meriwether, "I think Louisiana citizens all around the state heard me, and I think they understood me. They understood what I was saying."

He said he got an "outpouring" of prayers, which he called "humbling."

Vitter was asked if his "serious sin" broke the law. 

"You can ask those questions, you can look back 10 years, you can stay fixated on that — my job, I believe, is to look forward," he said.

The questions didn't stop.

"You may not like the answer I’ve given you," the senator added. Vitter was offered the opportunity to say yes or no on the question of whether he broke the law. "I'm not going to take that opportunity," he said, "because I think the people of Louisiana have understood exactly what I said to them."

Melancon accused Vitter of lying.

"Mr. Vitter has a problem with the truth," he said. "You just heard it. He would not admit that he lied, that he broke the law."

During the hour-long debate, both candidates took questions from a panel of reporters on issues ranging from immigration reform to the BP oil spill. It was their final meeting before Election Day on Nov. 2.