Senator John McCain called that "unacceptable." He said, "The American people deserve to know answers. And they certainly don't deserve false answers. And the answers that were given the American people on September 15th by the ambassador to the United Nations were false."

And McCain said Clinton must be more forthcoming about what really happened in Benghazi.

"There are many questions that are unanswered. And the answers frankly that you have given this morning are not satisfactory to me," he said.

Clinton said bringing to justice those responsible is more important than determining their motives.

​​​"The fact is we had four dead Americans," she said. "Was it because of a protest or was it because of guys out for a walk one night who decided they would go kill some Americans. What difference at this point does it make? It is our job to figure out what happened and do everything we can to prevent it from ever happening again."

Clinton said she needs Congress' help to see Libya's democratic transition through to a successful conclusion.

"Right now, Libya is still dangerous," she said. "It is still in a very unstable status. And whatever we can do for them we at least ought to agree we need to do and get out there and start delivering."

Cato Institute analyst Malou Innocent said U.S. challenges in Libya are substantial.

"Moving forward, we are still going to see a degree of chaos within Libya even as it has a veneer of a Western democracy," he said.