Obama would never be impeached, even if he murdered a man on TV.
The American Public does not tolerate a coward. If it comes out that Obama had actual knowledge of the requests for help from the victims at the time of the attack and that he did NOTHING to try and help them - then he is in deep shit.
At least half [if not more] of the country will believe he allowed them to be murdered - and that he is as culpable as the perps, by doing NOTHING.
If he had tried to help them, but was unsuccessful, that would be one thing. But, to have the ability to try - and then do NOTHING is unforgiveable.