Democratic presidential candidate and former Secretary of State Hillary Clinton testifies before the House Select Committee on Benghazi, Oct. 22, 2015, on Capitol Hill in Washington, D.C. The committee held a hearing to continue its investigation on the attack that killed Ambassador Chris Stevens and three other Americans at the diplomatic compound in Benghazi, Libya, on the evening of Sept. 11, 2012. Chip Somodevilla/Getty Images

Democratic presidential candidate and former Secretary of State Hillary Clinton testified Thursday before the House Select Committee on Benghazi to answer questions about her actions in 2012 when the American diplomatic compound in Benghazi, Libya, was attacked by terrorists and four Americans were killed, including U.S. Ambassador Chris Stevens. Republicans in Congress have been investigating the attack and appear determined to discover if Clinton acted inappropriately and if she did enough to prevent American deaths.

Thursday's hearing is one of the highest-profile events of the investigation, which has been criticized by Clinton and Democrats as being a partisan political event to throw off her chances to become president. It also comes after seven other congressional investigations of Benghazi. The current probe has hinged on several questions, including if there was anything that could have been done to prevent the attack, if President Barack Obama called back forces that could have helped, and if the White House lied about the nature of the attack. Last but far from least, a new question has arisen: Is this investigation merely a political attack on Clinton?

What Happened? On Sept. 11, 2012, Islamic militants attacked the Benghazi compound, breaking through the gates and setting the building on fire. As American security forces scrambled to evacuate the compound and move to a nearby CIA location, Stevens and Sean Smith, an information management officer with the U.S. Foreign Service, went missing and then died of smoke inhalation.

Once the security forces had made it to the CIA annex, a second attack resulted in the death of two CIA contractors as they returned fire.

What’s The Controversy? Stevens’ death was the first time an American ambassador was killed while on duty since 1979, prompting Republicans to raise concerns. The accusations party members levied are wide-ranging, including blaming the White House for telling backup security forces to stay down when the attacks were underway. They also claimed Obama mischaracterized the attacks and avoided calling them “terrorist” attacks, which became a key moment in the 2012 presidential campaign when Obama noted during a debate that he had, indeed, called them terrorist attacks. Republicans have also accused Hillary Clinton’s State Department of failing to provide adequate security and equipment beforehand to avoid the attacks.

Since the House Committee began, it was also discovered that Clinton used a private email server and address while at the State Department. The committee has said the emails are the reason the hearing had to convene so close to the primary voting season. Clinton had asked that the hearing be held sooner.

Are Those Republican Criticisms Valid? There is some gray area surrounding the accusation that the Obama administration looked to mislead the public about the event. Immediately after the attacks, the official White House narrative indicated they were the result of “spontaneous demonstrations,” meaning protesters who got violent. There is no evidence that any protests took place. The president did, however, the next day stand in the Rose Garden at the White House and characterize the ambush as a terrorist attack.

As for the accusations that the State Department failed to provide adequate security beforehand, four Americans died that day, so it is obvious there were shortcomings. The reasons for the inadequate security are contentious, however. The lack of security has been largely blamed on bureaucratic inefficiencies, and it has been noted that Clinton neither approved nor denied requests for additional security. The lacking security has also been blamed on the compound’s confusing status, since it wasn’t an embassy or an official consulate, and therefore wasn’t considered in budgetary matters in the way it would have if it were a more traditional post.

Are Republicans The Only Ones Upset About This? Clinton’s public image has been hurt heavily by this investigation, which could adversely affect her party's chances of nominating her for president. She was once seen as an almost inevitable primary nominee for the 2016 election. Her polling has dipped in large part because of the email scandal unearthed by the Benghazi committee. However, scant evidence exists that her emails contained sensitive, classified or damning information regarding Benghazi.

Democrats are also upset about the cost of the lengthy investigation, which is being paid for by taxpayers. The $4.7 million price tag associated with the probe prompted Senate Minority Leader Harry Reid and fellow Senate Democrats to send a letter this week to the Republican National Committee asking them to repay taxpayers.

Recently, House Majority Leader Kevin McCarthy, R-Calif., appeared to admit the House committee was political in nature. Speaking to Fox News, he said, “Everybody thought Hillary Clinton was unbeatable, right? But we put together a Benghazi special committee. A select committee. What are her numbers today? Her numbers are dropping. Why? Because she's untrustable. But no one would have known that any of that had happened had we not fought to make that happen.”

What Now? Clinton was expected to face intense pressure Thursday during the hearing, but the recent revelations of a possibly politically motivated probe show that Republicans will need to keep things as apolitical as possible. Either way, it’s unlikely that Republicans will simply drop the investigation should Clinton give a stellar performance.