Five questions on Hillary Clinton and the Benghazi committee

Hillary Clinton is set to testify in front of the House of Representatives Select Committee on Benghazi about the 2012 attack on the US consulate in the Libyan city that killed ambassador Chris Stevens and three other Americans.

It is the second time she has been called before Congress to discuss the raid by suspected Islamist militants on the US compound in Benghazi, which took place during her tenure as US secretary of state.

BBC state department correspondent Barbara Plett Usher has been following this complicated story and answered some of our readers' biggest questions about Benghazi on the BBC News Facebook page.

What does this committee do? What are the consequences for Clinton?

The committee is authorised to investigate and issue a final report on the Benghazi attacks: what hampered the government's ability to prepare for them and how it responded.

Clinton previous testified on the Benghazi attacks in 2013

As such it would be part of Congress' record on the attacks - including seven other congressional committees and a state Department investigation - which are meant to contribute to policy improvements.

But it would not have the power to punish anyone it criticises. However, depending on the conclusions there could be political consequences for Hillary Clinton, which might affect her presidential campaign

Why were we originally told US Ambassador Chris Stevens and three other Americans died because of a YouTube video that agitated a large crowd of people?

It's a good question, and one that was asked by numerous congressional investigations. There were demonstrations against the video in the region at the time, one of which targeted the US embassy in Cairo, and that's what the administration said also happened in Benghazi.

But many Republicans believed the White House was trying to deflect attention from what they saw as its policy failures in the battle against terrorism. The House Intelligence Committee agreed that the talking points were flawed. But it said intelligence analysts, not political appointees, made the wrong call, and there was no deliberate attempt at a cover up.

Why were the Ambassador's pleas for reinforcements ignored?

The US building in Benghazi on fire on 11 September 2012

Lack of security was a major focus of the State Department's internal investigation. One of its findings was that security was not recognised as a shared responsibility by the different bureaus in Washington charged with supporting the post, so they didn't talk to each other or make decisions together.

It also found that the embassy in Tripoli didn't strongly advocate for increased security in the Benghazi special mission. As for Hillary Clinton, she's said in previous testimony that requests for additional security didn't reach her level. But she has taken responsibility for the failure. And the State Department review laid out steps to improve security at diplomatic missions.

However, this issue will come up in the Benghazi hearing on Thursday. The committee chairman has said emails show Clinton's staff had other political priorities than responding to the ambassador's pleas.

Isn't this the sixth congressional committee to investigate her? Didn't the first five find nothing against her?

This is the eighth congressional investigation. Previous committees criticised Mrs Clinton and the Obama administration on a number of points, especially the poor security at the Benghazi mission.

They also said early intelligence reports about the attacks were contradictory and the administration's talking points were flawed. However, the House Intelligence Committee found no evidence of a deliberate cover up, and said the military and CIA responded properly to the attacks.

An internal State Department investigation has since laid out steps to improve security at diplomatic missions, but State Department officials have said lack of money didn't play a role in the attack.

Is there anything left to discover?

Rep Trey Gowdy faces pressure to deliver more than previous investigations into the attacks

The Republican chairman of the committee, Trey Gowdy, says yes. He says the committee has unearthed 50,000 documents never seen by Congress - including not only Clinton's emails on Benghazi and Libya, but those of the ambassador who was killed. The committee also interviewed 41 witnesses who have never testified to Congress on this topic, including seven eyewitnesses.

He has suggested there is more evidence of how poorly the state department responded to security requests for the Benghazi mission, and new evidence on how the military responded to the attack. How much of that will add substantially to the record is not clear. But he'll be under pressure on Thursday to demonstrate that his is a substantive investigation rather than a partisan attack on Mrs Clinton.

Questions and responses have been edited for clarity.