The month after Obama was re-elected, an independent review board issued its harsh verdict.
Senior officials in Washington had failed to protect the Benghazi mission, even after diplomats in Libya asked for more security, said the panel appointed by the State Department.
Since the overthrow of dictator Moammar Gadhafi, eastern Libya has been plagued by violence and awash with heavily armed militias. The U.S. compound as well as British diplomats and the Red Cross had been targeted by explosives in smaller attacks several times over the spring and summer.
The danger was obvious.
And yet security was "inadequate for Benghazi and grossly inadequate to deal with the attack that took place," the Accountability Review Board concluded.
Four State Department officials were reassigned or resigned as a result.
"We clearly fell down on the job with regard to Benghazi," Deputy Secretary of State William Burns told lawmakers.
Republicans put the focus on Clinton's responsibility. In combative congressional hearings in January, the outgoing secretary of state said the cables from Benghazi seeking help never reached her.
"I did not see these requests. They did not come to me," she said. "I did not approve them. I did not deny them."
Obama called the poor security "a huge problem" and said changes would be made to protect risky posts.
Democrats tried to shift some blame to congressional Republicans, complaining that they cut $300 million from the Obama administration's budget request of $2.6 billion for diplomatic and embassy security in 2012.
WHERE WAS THE CAVALRY?
Could the military have done more to help on Sept. 11? A former top diplomat thinks so.
Gregory Hicks, who was Stevens' No. 2 and monitoring the crisis from Tripoli that night, suggests that sending fighter jets or even a cargo plane overhead might have scared off the insurgents with a show of force. That might have saved the lives of the two CIA contractors by preventing the final assault on the CIA annex, which came about eight hours after the first attack on the diplomatic mission, Hicks told a House committee.
Hicks also said four members of a special forces team in Tripoli wanted to fly on a Libyan plane to Benghazi but were told to stand down. Pentagon officials said the evacuation was already beginning by then and those forces would have arrived too late.
Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told the Senate there wasn't enough information about what was happening on the ground to send in aircraft. For example, for several hours officials didn't know what had happened to the ambassador.
Former Defense Secretary Leon Panetta made the same point. "You can't just willy-nilly send F-16s there and blow the hell out of a place without knowing what's taking place," Panetta told senators.
State's review board concluded the military did what it could. An unarmed Predator drone flew over the diplomatic post beginning shortly after 11 p.m. to gather information. Two military personnel were with the team from Tripoli that arrived at the CIA annex in the morning. A C-17 from Germany carried the evacuated Americans out of Tripoli. Special operations forces and other personnel who were deployed from Europe and the United States in response to the crisis didn't reach Libya in time to help.
"The interagency response was timely and appropriate," according to the review board, "but there simply was not enough time given the speed of the attacks for armed U.S. military assets to have made a difference."
The FBI is still investigating who carried out the attack, and Attorney General Eric Holder says there has been "very, very substantial progress."
Republicans on five House committees are pursuing inquiries. Many GOP lawmakers are pushing House Speaker John Boehner, R-Ohio, to appoint a special select committee to investigate.