The attack on Al-Baghdadi was a replay of the Camp Leatherneck fight.

via RT

The Islamic State carried out a coordinated suicide bomber attack against the air base in western Iraq housing 320 US Marines. The Pentagon confirmed the extremist group has taken control of al-Baghdadi, which is just eight kilometers away from the base.
The Friday attack was conducted by approximately 25 Islamic State fighters, the Pentagon told Reuters, and several suicide bombers were involved. Some of them were reportedly able to detonate their vests, though the exact number is unclear. Some of the militants were able to sneak into the base wearing Iraqi uniforms, and they were killed by Iraqi troops when fighting broke out.

This is just an open source look at what happened during the attack, but it appears to me that ISIS tried a replay of the attack on Camp Leatherneck when they hit Al-Baghdadi.

And they're showing us the achilles heel of our Pentagon strategy globally.

These partnership/training missions are fraught with peril because we're embedding our forces into situations where the vetting of host nation personnel is sometimes shoddy, sometimes politically motivated and always dangerous because we never know who we're working with.

If I was in charge of force protection for our Marines, I would dedicate at least half the force assigned to these training missions to internal security.  Whether that's assigning Marines to overwatch positions while others are teaching, to having a guard force inside the guard force while Marines are in barracks, to having a separate reaction force both on the ground (where the training is taking place) with an additional force ready to fly in....this is the point of vulnerability that I see ISIS going for.

Insider attacks.

It's how ISIS will go after our forces.