WATCH: Hillary Clinton stays cool during heated Benghazi exchanges
In testimony that stretched deep into the night, the former secretary of state rejected Republican accusations that she ignored requests for security upgrades in Libya.
Democratic presidential candidate Hillary Clinton passed a tough political test on Thursday, calmly deflecting harsh Republican criticism of her handling of the deadly 2012 attack in Benghazi, Libya, during a testy 11-hour hearing in Congress.
In testimony that stretched deep into the night, the former secretary of state rejected Republican accusations that she ignored requests for security upgrades in Libya and misinformed the public about the cause of the attack by suspected Islamist militants that killed the U.S. ambassador and three other Americans in Benghazi.
Clinton said it was "personally painful" to be accused of ignoring security upgrades that could have saved the life of ambassador J. Christopher Stevens and three other Americans at the diplomatic compound.
"I've thought more about what happened than all of you put together," she told the Republican-led special panel. "I've lost more sleep than all of you put together. I've been racking my brain about what could have been done, should have been done."
The appearance before the Benghazi panel was a critical hurdle for Clinton, who has been on a hot streak since turning in a strong performance at last week's first Democratic debate and after Wednesday's news that her strongest potential challenger, Vice President Joe Biden, will not seek the Democratic nomination for the November 2016 election.
Even some Republicans said Republican lawmakers had swung at Clinton and missed with their aggressive questioning.
"They forget Secretary Clinton has been dealing with hostile committees longer than most of them have been in politics at any level," Texas-based Republican strategist Joe Brettell said.
Opinion polls show Americans deeply split along partisan lines over the probe. A Reuters/Ipsos poll this week found 35 percent of respondents viewed the Benghazi hearings as mostly or completely valid. The percentage among Republicans was 67 percent, independents 39.6 percent and Democrats 16.5 percent.