As I recall we been down this path. It IS policy, IIRC, to “wait for back up. This ain’t the first time.
After Columbine and VaTech, it was more or less held that first responders would wait for tactical units. As these incidents began to happen more and more, the training doctrine has changed.
The DHS doctrine, which is pretty much the same as everyone else’s is:
If you hear gunfire, you make entry, locate and confront the threat. Alone if you have to. You do not wait.
If you do not hear gunfire, you wait for the first back up officer and the two of you make entry and do what you can, communicating with others on the way.