Secretary Clinton says the attack on the U.S. mission in Benghazi that killed four Americans, including the ambassador, is part of a broader strategic challenge in the fight against terrorism.
"The Arab revolutions have scrambled power dynamics and shattered security forces across the region," she said.
"And instability in Mali has created an expanding safe haven for terrorists who look to extend their influence and plot further attacks of the kind we saw just last week in Algeria.
Clinton told lawmakers she has accepted all of the recommendations of an independent review board, 85 percent of which will be completed by the end of March.
"We are taking a top-to-bottom look, and rethinking how we make decisions on where, when, and how our people operate in high threat areas, and how we respond to threats and crisis ," she said.
Political fall-out over the response to the Benghazi violence focused on U.N. Ambassador Susan Rice, who gave a series of television interviews shortly after the attack - linking it to Islamist protests , not a terrorist attack.
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.
Whatever can be done to reduce threats to U.S. diplomats abroad, Clinton said they accept a level of risk in their work and cannot do their jobs from bunkers.
We made a strategic withdrawal, so that we could build up our forces for a renewed attack.
A table was pushed over in the scramble.
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Half a million people held a mass protest against racism last night.
The efficacy of the medicine is satisfactory.