Could Benghazi impact Hillary Clinton in 2016?

Updated at 3:19 p.m. ET

When Hillary Clinton testified in January about the State Department's response to the terrorist attacks in Benghazi, she grew frustrated with questions over what caused the violence and exclaimed "what difference at this point does it make?"

On Wednesday, she may have gotten her answer - at least in terms of politics.

Three State Department officials offered testimony before the House Oversight Committee that was emotional and riveting. It was the first time the public had heard from someone who had been on the ground in Libya the night terrorists stormed a U.S. diplomatic outpost and killed Ambassador Christopher Stevens and three others. Prodded by several of their Republican questioners, the witnesses leveled serious accusations at Clinton and her staff.

• Benghazi "whistleblowers" question U.S. reaction to Libya attack
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Gregory Hicks, the number two diplomat at the U.S. Embassy in Tripoli, described being in constant contact with then-Secretary of State Clinton the night of September 11, 2012. And yet he said his requests for military resources to be deployed to Benghazi were repeatedly denied. The Obama administration says any planes or special forces would not have gotten to the attack site in time to help. Hicks also said that in the aftermath of the attacks, one of Clinton's top aides berated him for meeting with a congressman without a State Department lawyer present. Hicks added that he believed he had been demoted because he had spoken out.

Republicans say they just want to know what happened in Benghazi and why. But with Clinton seen as the leading contender for the Democratic nomination in 2016, the GOP investigation is also a chance to highlight a black mark on her record and try to bring down some of her currently sky-high poll numbers.

"I think she just spent how many years as secretary of state and she's going to run with that being on her resume and these questions are directly related to her experience," says Republican National Committee spokeswoman Kirsten Kukowski. Since the hearing, the RNC has emailed reporters several press releases about Clinton's role in the response to the attacks.

Democrats say this is a familiar playbook for Republicans and it won't sully the former secretary's reputation.

"They cannot separate politics from governing. This is a case where before leaving office, she took responsibility, it was well investigated, [and she] admitted there were flaws in the system," says Mo Ellleithee, who worked on Clinton's 2008 presidential campaign. "I think people get what happened and I don't see it having the kind of political impact that the other side is hoping it has."

Clinton herself has not commented on Wednesday's hearing. But in an email to MSNBC, her longtime aide Philippe Reines said the proceedings amounted to a partisan witch-hunt.

"He could've asked Hicks about his favorite color and Jordan would have blurted out 'cover up' in response," Reines wrote about Rep. Jim Jordan, R-Ohio, whose questioning led Hicks to describe being scolded over the phone by Clinton staffer Cheryl Mills.

For the most part, Clinton stayed out of political fights while she served as secretary of state. And in turn, Republicans focused their attention on her boss, President Obama. Wednesday's hearing marked the official end of that detente. Congressional Republicans have promised more hearings and further investigations. If the long history of the adversarial relationship between Republicans and the Clintons is any guide, that could have significant implications for 2016.

Here's what else the 2016 contenders have been up to this week:

Vice President Joe Biden:  Biden made news on several of the Obama administration's key initiatives this week. First he suggested there would be a renewed push for gun control legislation - something he said he still had not spoken to the President about. He later clarified any gun control push would come after Congress completes its work on comprehensive immigration reform. The Sierra Club, an environmental advocacy group, also posted on its website that Biden told one of its members he did not support the Keystone XL Pipeline. He added, however, that he was "in the minority."

Gov. Martin O'Malley, D-Md.: O'Malley is dealing with the fallout from the indictment of 13 correctional officers and 12 inmates at a Baltimore prison for gang-related activities such as smuggling drugs into the jail and laundering money. On Thursday, O'Malley announced a series of measures to help root out corruption in prisons. The proposals include installing cell phone suppression technology at the jails and requiring prison staff to undergo lie-detector tests.

Sen. Elizabeth Warren, D-Mass.: The freshman senator this week introduced her first piece of legislation. The Bank on Students Loan Fairness Act would allow students to receive interest rates on their loans in line with what major banks get from the Federal Reserve.

Sen. Kirsten Gillibrand, D-N.Y.: Gillibrand is leading the fight again sexual assaults in the military. After the man tasked with preventing sexual assaults in the Air Force was himself arrested and a new report showed a sharp increase in the number of sexual assaults in the military, Gillibrand vowed to introduce legislation to combat the problem. On Thursday, she attended a White House meeting on the issue along with fellow 2016 contenders Sen. Amy Klobuchar, D-Minn., and Sen. Kelly Ayotte, R-N.H.

Gov. Chris Christie, R-N.J.: Christie announced this week that he had undergone weight-loss surgery back in February. He said he made the decision because of his family, but many also saw it as a sign he was gearing up for a future presidential campaign. The announcement overshadowed some disappointing business news for New Jersey. The rental car company Hertz said it would move its headquarters from the Garden State to Florida.  Barbara Buono, Christie's Democratic opponent in this year's gubernatorial race, seized on the announcement as a sign Christie's economic policies aren't working.

Gov. Bob McDonnell, R-Va.: So far, McDonnell does not seem to be suffering any negative fallout from a report that he's being investigated for gifts he received from a wealthy donor. A new Washington Post poll finds 64 percent of Virginia voters approve of the job their governor is doing. Only 32 percent say they are following the scandal somewhat closely.

Sen. Marco Rubio, R-Fla.: Rubior continued his push for comprehensive immigration reform this week. Ahead of the Judiciary Committee's markup of proposed legislation, Rubio met privately with grassroots conservatives to rally support. On Thursday's "CBS This Morning," he took issue with a report from the conservative think tank the Heritage Foundation that found the bill would cost $6.3 trillion over five decades. "The study is not a legitimate study," he said.

Gov. Bobby Jindal, R-La.: The Louisiana Supreme Court ruled this week that Jindal's school voucher program was unconstitutional. The program gave public funds to thousands of students to pay for private education. In a statement, Jindal said "we're disappointed the funding mechanism was rejected, but we are committed to making sure this program continues and we will fund it through the budget." Jindal is attending a Republican fundraiser in New Hampshire on Friday.

Sen. Rand Paul, R-Ky.: Paul makes a high-profile early state visit Friday with a stop in Iowa. He's in Cedar Rapids to speak at the Iowa Republican Party's Lincoln Day Dinner.

Editor's note: An earlier version of this article said diplomat Gregory Hicks testified he was yelled at by Hillary Clinton staffer Cheryl Mills. Hicks actually described the tone of Mills' voice had indicated to him "very strongly that she was unhappy." The article has been updated to more accurately reflect Hicks' recollection of Mills' tone.