Clicker Training w/ Trooper the Rescue Horse

Trooper, a recent Off the Track Thoroughbred (OTTB) rescued horse from the kill pen shows us fear, aggression towards grooming brushes - due to his unknown, traumatic past.
We are using "targeting" and clicker training/positive reinforcement to help him understand the brushes will never harm him here. With consistency we are hopeful he will learn to trust and we can groom him safely, peacefully; and that the trust will be reciprocal.