Secretary of State Hillary Clinton will finally take questions from members of Congress on Wednesday about the deadly terror attack on the U.S. diplomatic mission in Benghazi, Libya.

Lawmakers have long wanted Clinton's full accounting of the Sept. 11 assault that killed Ambassador Christopher Stevens and three other Americans.

They also want to ask her about diplomatic security, which the State Department has since re-examined at posts located in overseas hot spots. Agency officials have acknowledged shortcomings and promised changes.

Some of the toughest questions before the House Foreign Affairs Committee and the Senate Foreign Relations Committee are expected to focus on the Obama administration's slow-to-evolve public explanation of the attack, which triggered an uproar in the middle of a presidential election campaign.

U.N. Ambassador Susan Rice took most of the political heat as mainly Republican lawmakers seized on her public comments the administration has said were based on fast-moving intelligence that later proved to be incorrect.

Still, some Republicans suggested the administration sought to mute the true nature of the attack to prevent President Barack Obama's political opponents from fully exploiting it in the final weeks of the November campaign.

The issue was so polarizing that Clinton's decision to postpone an initial appearance before Congress in December due to health problems was questioned by her harshest critics as a possible dodge.

It was revealed that she had a virus and suffered a concussion. Clinton was then hospitalized for a blood clot, only returning to work two weeks ago.

Her testimony will be public and will likely be the most difficult moment of her final days as America's top diplomat.

Despite the controversy, Clinton's poll numbers remain high.

Some of the potential questions she will face:

What did Clinton know?

Republican Sen. John McCain wants a full explanation of Clinton's understanding of the attack -- what happened before, during and after.

The 2008 GOP presidential nominee and the top Republican member of the Senate Armed Services Committee, McCain told CNN this week that he feels "the American people were clearly deceived."

McCain told reporters eight days after the attack that he had information the State Department had been warned.

In mid November, McCain took to the floor of the Senate and accused Obama of lying about the attack.

"The American people have received nothing but contradictory statements from all levels of our government," he said.

The Pentagon released an official timeline that highlighted when Defense Secretary Leon Panetta and his senior commanders were first informed and when follow up decisions were made involving the military.

The timeline shows Panetta and Joint Chiefs Chairman Gen. Martin Dempsey were told of the attack about an hour after it started. Both were on their way to the White House for an already scheduled meeting with the president. Thirty minutes later, Obama was directing the Pentagon to do all it could to help, according to senior Pentagon officials.

What does Clinton know about cables warning of security threats?

Just hours before the attack, Stevens sent a message to the State Department that referred to a meeting nine days earlier during which the commander of Benghazi's Supreme Security Council "expressed growing frustration with police and security forces" about security capabilities.

That cable, since made public, is part of more than 160 pages of documents that paint a picture of persistent and unpredictable violence in and around Benghazi last year. It also reveals that the U.S. contingent in Benghazi felt it needed more security.

In February, the regional security officer in Tripoli, Eric Nordstrom, warned that having just two diplomatic security agents on the ground in Benghazi made movements outside the U.S. facility impossible.

"I've been placed in a difficult spot when the ambassador tells me I need to support Benghazi," Nordstrom wrote in a Feb. 12 email to the regional director of the Near East Affairs Department at the State Department.

Was Clinton informed about the rise of al-Qaida-linked militants?