Do enemies have a predetermined portal destination when there are more than one portal in the first Orcs Must Die!?

I'm playing the original Orcs Must Die!.

I'm on a level called The Library.

There are 2 portals and 2 doors for the enemies to come from.

If I blocked one of the portals with barricades, would enemies destroy those barricades or would all of them try to reach the other portal?