Trying to buck the stream of ISIS combatants is like trying to turn aside the Red Chinese pouring into North Korea. There are so many that should one fall, there is another immediately behind to pick up the weapons of the fallen ones and continue to advance.
Like a swarm of locusts.
I believe that is exactly wrong. There at most 5000 ISIS fighters. They will struggle to hold what they win and Bagdad will most likely be too much for them.