The former Navy Seals who died on a roof were killed by terrorist mortar fire. They gave up their position to the jihadis by laser-painting a target on the mortar nest, expected that their targeting it would be swiftly followed by a US air attack that never came.
The facts about Benghazi are these:
1. Obama knew of Jihadi activity in the region thirty days before the attack. He took no precautions and did nothing to improve security.
2. Obama knew the nature of the jihadi attack in real time as it unfolded but took no action nor gave any orders to the military to take any action to save the embassy staff. In fact, he ordered the CIA to "stand down," meaning, "do nothing." This, in spite of the fact that two drones and a helicopter gun ship were overhead.
3. Obama apparently failed to act on behalf of the embassy staff for ideological and political reasons. Karen McQuillan, writing at the American Thinker writes:
Obama does not believe in using the military to defend our national security, which he sees as aggressive, Republican, and cowboy. This was Obama's 9/11, not Bush's. He did not see the attack on our embassy as a jihadi attack on American soil. He saw a group of aggrieved Muslim citizens, with good reason to be angry -- the spontaneous mob enraged by an offensive video. He would follow a Democrat policy of promoting peace, not war, in which avoiding civilian casualties is the paramount goal.In other words, Barack Obama was willing to sacrifice the lives of 37 embassy personnel through inaction and gross negligence, in pursuit of a leftist ideology. (Due to CIA Agent Tyrone Woods disobeying orders to "stand down," only four were killed -- including Woods.) If the truth were known, the American people would ride Obama's worthless butt out of DC on a rail. The mainstream media, of course, will not allow that to happen.
The other answer is directly political. It would be damaging for Obama's already weak record to admit that there was a 9/11 attack by al-Qaeda in one of the supposed successes of the Arab Spring. Responding militarily would have made the weaknesses of Obama's foreign policy all too evident. An American military response would have undercut one of Obama's main campaign slogans: "GM is alive and Osama is dead."
Read the entire article, Why Obama Chose to Let Them Die in Benghazi.