Secretary of State Hillary Rodham Clinton likely will face tough questions about the deadly Sept. 11 terrorist attack on the U.S. mission in Benghazi, Libya — including how the U.S. ambassador went missing for several hours during the assault — when she meets Wednesday with the House and Senate foreign affairs committees.

The appearance, likely to be her last before Congress, will cap her time as secretary of state by revisiting one of the most bitterly contested and controversial episodes of her tenure.

Some Republicans have charged that the Obama administration deliberately blurred or tried to hide the fact that the attack was the work of terrorists linked to al Qaeda, who killed Ambassador J. Christopher Stevens and three other Americans.