noonan does a good job of summing the situation up, it fact, hits the nail on the head.
The Inconvenient Truth About Benghazi
Why couldn't the administration tolerate the idea that Benghazi was a planned terrorist event? Because they didn't want this attack dominating the headline with an election coming. It would open the administration to criticism of its intervention in Libya. President Obama had supported overthrowing Muammar Gadhafi and put U.S. force behind the Libyan rebels. Now Libyans were killing our diplomats. Was our policy wrong? More importantly, the administration's efforts against al Qaeda would suddenly come under scrutiny and questioning. The president, after the killing of Osama bin Laden, had taken to suggesting al Qaeda was over. Al Qaeda was done. But if an al Qaeda offshoot in Libya was killing our diplomats, the age of terrorism was not over.
The Inconvenient Truth About Benghazi - WSJ.com