Bitter political undercurrents festered all day during a contentious showdown that turned into a political endurance test. After a day-long grilling on the details of the attack and how Clinton handled it, the former secretary of state was forced to defend her use of a private email account while in office from a flurry of late evening attacks by GOP lawmakers.
She also came under testy cross-examination over the extent to which she has taken responsibility for the deaths of the Americans in the September 11, 2012, attacks and her contact with U.S. Ambassador to Libya Chris Stevens, one of the victims, after sending him to the North African country.
"I came here because I said I would. And I've done everything I know to do, as have the people with whom I worked, to try to answer your questions. I cannot do any more than that," Clinton said towards the end of the grueling day -- before later breaking into a coughing fit and taking a throat lozenge to ease her failing voice.
The performance, coming one day after Vice President Joe Biden's decision not to seek the presidency and a week after a strong showing at the Democratic debate, could solidify Clinton's standing as the prohibitive favorite to win her party's presidential nomination.
The morning after the hearing, Clinton HQ was "ecstatic," according to one source, a Clinton campaign aide who added "that was a president sitting there."
While the hearing did not appear to include any major new revelations on what happened In Benghazi or Washington on the night of the attack, it did offer an opportunity for Republicans to probe what they say are still unanswered questions about the tragedy.
And so deep is the partisan divide over the attack that the exhaustive hearing is unlikely to have changed many minds. Republicans are sure to still view Clinton as resistant to scrutiny and to blame her for security lapses in Benghazi. Democrats are sure to continue to see the hearing as a witch hunt designed to wound the Democratic front-runner's 2016 campaign.
One Republican, Rep. Peter Roskam of Illinois, grew increasingly frustrated about Clinton's refusal to provide any new answers on the attack.
"I have heard one dismissive thing after another. What did you do? What did you own?" Roskam asked, his patience fraying over Clinton's repeated statements that though she accepted responsibility for what happened in Benghazi, decisions about security arrangements were left to U.S. envoys on the ground and security professionals in the State Department.
Roskam ripped a piece of paper in two in a theatrical gesture meant to support his claim that requests for security from Stevens were denied.
"You laid this on Chris Stevens, didn't you? They didn't get through to you. They didn't get through to your inner circle," Roskam charged.
One of the most dramatic moments of the hearing came when Clinton was asked about her contact with Stevens. She acknowledged that she couldn't recall having talked to him after having sworn him in as ambassador, though she believed they had spoken.
Despite the day's intensity, Clinton appeared cool and in command for much of the hearing. But as the day wore on, she seemed to be increasingly impatient with the Republican line of questioning and with the constant interruptions from the GOP members on the panel.
In her most emotive testimony, Clinton sought to defang the GOP attacks by arguing that she agonized over the deaths of four Americans in Libya more than anyone else on the panel.
"I would imagine I have thought more about what happened than all of you put together," she said. "I have lost more sleep than all of you put together. I have been wracking my brain about what more could have been done or should have been done."
Ohio Rep. Jim Jordan repeatedly attacked Clinton throughout the day, first alleging that she and other Obama administration staff tried to blame the attack on the consulate on an anti-Muslim YouTube video to avoid undercutting President Barack Obama's claims that he had crushed al Qaeda.
"You could live with a protest about a video, that won't hurt you, but a terror attack would," Jordan said, saying that Americans could accept, reluctantly, compatriots being killed abroad but "what they can't live with is when their government is not square with them."
Clinton rejected the claim, saying in the desperate hours after the attack, that information on the true nature of the assault on the compound by a mob was unclear.
"I am sorry that it doesn't fit your narrative congressman, I can only tell you what the facts are."
Jordan also clashed with Clinton over her use of a private email server she employed instead of a government account while secretary of state.
"It seems like there is a pattern, a pattern of changing your story ... If your story about your emails keeps changing, how can we accept your statements that you have turned over all work-related emails and all emails about Libya?" asked Jordan.
The lawmaker became exasperated when Clinton said that the email server was on her property, guarded by the Secret Service. He asked how that would thwart a hacking attempt and demanded to know why she brought it up. Clinton replied that she had been motivated to do so "out of an abundance of being transparent."
Clinton also came under repeated criticism from Republicans who didn't accept her explanations as they tried to prove she ignored pleas from U.S. diplomats in Libya for better security and played the dominant role in the U.S. intervention in Libya, which was an initial success but left a chaotic failed state behind.
The hearing evolved into a tussle between Republicans who believe there are still serious questions to answer about what happened in Benghazi -- as well as those who appear to want to dent her presidential ambitions -- and Clinton as she tries to build on a resurgence in her campaign after a tough summer.
At one point, the panel's top Republican, Trey Gowdy, and Democrat, Elijah Cummings, began shouting and interrupting each other over what information the committee should release while Clinton sat silently in the witness chair, watching the heated exchange and nodding her agreement with Cummings.
And as the evening wore on, Democrats became increasingly impatient for the hearing to end.
"We are better than using taxpayer dollars to try to destroy a campaign," Cummings fumed. "That is not what America is all about."
Clinton replied that her answers had been no different than when she testified before the House and Senate on Benghazi two years ago, then slipped into campaign mode: "I realize there are many currents at work in this committee, but I hope that the statesmanship overcomes partisanship. At some point we have to do this."
Another Republican, Rep Mike Pompeo of Kansas, tried to rile Clinton by asking why her old friend and political operative Sidney Blumenthal had been able to send her personal emails, requests for more security from U.S. staff in Libya did not reach her desk.
Clinton responded by saying that she had accepted that she was responsible for sending Americans into harm's way, but she maintained that the exact details of operational security had been left to professionals within the State Department and were not within her purview.
"i was responsible for quite a lot," Clinton said. "I was not responsible for specific requests and security provisions -- that is not something I was responsible for."
Clinton's calm demeanor cracked under an early evening line of questioning from Alabama Rep. Martha Roby, who wanted to know what she was doing after she left the office and went home from the State Department on the night of the attack.
"I was alone," said Clinton, who seemed surprised by the question.
"The whole night?" asked Roby. "Yes, the whole night," Clinton said before launching into her famous guffawing laugh.
"I don't know why that is funny. Did you have an in-person briefing?" Roby asked.
Clinton, looking at a clock on the wall, replied: "I'm sorry, a little note of levity at 7.15," before assuring Roby she didn't sleep on that fateful night and was in constant contact with aides via a secure phone line.
There were several occasions when Democrats teed up questions for Clinton that allowed her to speak at length and in personal terms about the events in Benghazi.
At the prompting of Cummings, Clinton spoke movingly about the deaths of Stevens and State Department Information management officer Sean Smith from smoke inhalation.
With an eye on the audience outside the Capitol Hill hearing room, Clinton said that she wanted members and "viewers in the public to understand this was the fog of war" in the confused hours after the attack.
And she related how a security agent with Smith and Stevens had "turned back into that diesel smoke desperately trying to find Chris and Sean. He did find Sean and Sean had succumbed to smoke inhalation ... He could not find Chris Stevens."
Her allies on the committee also repeatedly raised questions about the integrity of the investigation. One lawmaker, Adam Schiff of California, said the only reason Clinton was in the room was because she was running for president and had high poll numbers.
But throughout, Republicans maintained that the panel was not created to serve partisan ends.
Gowdy rejected Democratic claims he was leading the investigation to a pre-ordained verdict with the intention of damaging Clinton.
"There is no theory of the prosecution," Gowdy said, raising his voice.
"This is not a prosecution," he reiterated moments later. "I have reached no conclusions."
But the heated exchanges highlighted that the hearing is not only limited to an examination of Clinton's record on Benghazi but also the extent to which partisanship has shaped the investigation, with the Democratic candidates' allies repeatedly charging the GOP with politically motivated maneuvers.
Roskam also accused Clinton of using the U.S. intervention in Benghazi to boost her own personal political brand.
"Let me tell you what I think the Clinton doctrine is -- I think it is where an opportunity is seized to turn progress in Libya into a political win for Hillary Rodham Clinton, and at the precise moment when things look good, take a victory lap like on all the Sunday shows ... and then turn your attention to other things," Roskam said.
The former secretary of state quickly seized on that comment to further her contention that the hearing was nothing but political grandstanding.
"That is only a political statement which you well understand, and I don't understand why that has anything to do with what we are talking about today," she said.
Cummings claimed the probe had wasted 17 months and $4.7 million on a partisan fishing expedition that had turned up no new evidence on the attack, which occurred when she was secretary of state.
Clinton noted that an independent Accountability Review Board that she set up as secretary had pulled no punches, unveiling 29 recommendations for improving security for U.S. diplomats overseas. She also noted that previous attacks on Americans abroad, including in 1983 on a U.S. Marines barracks and the U.S. Embassy in Beirut, had produced changes to U.S. security procedures after nonpartisan investigations by Congress.