Secretary of State Hillary Clinton offered an unwavering defense Wednesday of the Obama administration's response to the 2012 assaults on U.S. government posts in Benghazi, Libya.
Mrs. Clinton again took responsibility for any security lapses in Benghazi but praised the response from her department and other government agencies.
She said the attacks "are part of a broader strategic challenge to the United States and our partners in North Africa" because of the emergence of violent extremism there.
As she began her testimony, Mrs. Clinton became visibly emotional as she recalled meeting relatives of U.S. Ambassador Christopher Stevens and three other Americans who were killed in the Sept. 11 assault.
"I stood next to President Obama as the Marines carried those flag-draped caskets off the plane at Andrews [Air Force Base]," she told senators, choking back tears. "I put my arms around the mothers and fathers, sisters and brothers, sons and daughters."
Her appearance before the Senate Foreign Relations Committee had valedictory overtones, as she plans to step down once Sen. John Kerry (D., Mass.) has been confirmed as the new top diplomat.
"It has been one of the greatest honors of my life to lead the men and women of the State Department and USAID (U.S. Agency for International Development)," she said.
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After listing a battery of government reactions to the Sept. 11 assault in Libya, she praised the work force of her agency.
"They ask what they can do for their country," she said.
Mrs. Clinton also is scheduled to testify before the House Foreign Affairs Committee about the Benghazi attacks.
That hearing, like its Senate counterpart, will be public.
The grueling day of testimony comes as Mrs. Clinton recovers from a month of health problems that began with a stomach virus and ended with her hospitalization for a blood clot near her brain. She has been back at work for two weeks, holding meetings, placing phone calls and making several abbreviated public appearances.
State Department officials said Mrs. Clinton expected to face tough questioning from lawmakers, especially Republicans, who have assailed the Obama administration's missteps on the attacks.
Adding an extra note of potential political drama, the Senate panel includes a possible 2016 GOP presidential candidate, Sen. Marco Rubio of Florida. Mrs. Clinton, a Democrat, also is frequently mentioned as possible presidential contender.
GOP lawmakers have demanded to know what Mrs. Clinton did to improve security at the U.S. diplomatic post, and they maintain the administration attempted to deceive the public about the nature of the assault.
Soon after the assault, Mrs. Clinton took responsibility for inadequate security, but she has rebuffed questions from lawmakers until now, deflecting them for weeks while an investigation by an independent Accountability Review Board was under way.
That probe was completed last month and released while Mrs. Clinton was recuperating. It found that the State Department's response to the Benghazi attacks showed "systemic failures" in handling consular security.
The board faulted a "lack of proactive senior leadership" for security in Benghazi and said physical security was "profoundly weak."
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Department officials accepted the board's findings and have agreed to enact all 29 recommendations in the report. The department dispatched teams of diplomatic and military officials to assess 19 high-threat posts and recommend security arrangements for each one.
A second investigation, by the Senate Homeland Security and Governmental Affairs Committee, formed the first bipartisan congressional report on the Obama administration's response to the Benghazi attacks.
The committee's report, issued Dec. 31, found that the State Department and Pentagon had no viable way to rescue Americans in Benghazi and the State Department had repeatedly failed to learn from past security breaches at embassies. The report spread the blame beyond State to include the Pentagon and the Obama administration.
Mrs. Clinton's appearance Wednesday followed dozens of public and closed-door sessions on Capitol Hill focused on the Sept. 11 assaults.
A confirmation hearing for Mr. Kerry will be held Thursday, before the same Senate committee that interviewed Mrs. Clinton.