Democratic presidential contender Hillary Clinton is set to testify in front of a Congressional committee about the attack on a US consulate in Libya in 2012 that killed the US ambassador and three other Americans.
She was secretary of state at the time and is likely to face tough questions.
This is Mrs Clinton’s second appearance before Republican-dominated Congress on her handling of the incident.
Her party says it is a witch-hunt designed to harm her presidential bid.
There have already been seven congressional investigations into the attack, by suspected Islamist militants, on the US compound in the Libyan city of Benghazi on 11 September 2012.
The raid led to the deaths of ambassador Chris Stevens and three other US embassy staff.
Mrs Clinton is likely to be asked to explain:
- Why the US government initially claimed the attack was spontaneous, sparked by a YouTube video that had led to protests in the region, when evidence later emerged that the raid was likely to have been planned
- Why calls by ambassador Stephens for security reinforcements at the consulate were apparently ignored
- Whether she compromised classified information by using her private email server instead of using a government email account for all her correspondence while secretary of state
Observers say this is a key moment for Mrs Clinton, who solidified her position as the Democrats’ frontrunner for presidential candidate after her potential rival, Vice-President Joe Biden, ruled himself out of the race on Wednesday.
Her appearance before the House of Representatives Select Committee on Benghazi could further strengthen her position or raise doubts about her suitability as a presidential nominee.
The Republicans on the committee are also under pressure to prove they have good reason to bring Mrs Clinton before them, and are not just using it as an excuse to undermine her presidential candidacy.
Comments made by Republican Representative Kevin McCarthy earlier this month, as part of his bid to become Speaker of the House, suggesting the committee was doing just that, have not helped their position.
Mrs Clinton said, in a television interview earlier this month, that she was “looking forward to answering questions about the real things when I’m there” and voiced her disgust at “a political partisan committee for the sole purpose of going after me”.
One of the Republicans on the committee dismissed any suggestion it was partisan. “This has never been political for us,” Martha Roby told the Associated Press. “This has always been about finding out the truth.”