A portable, tactical building door opener comprises a door opening mechanism comprising: a body; a door opening arm pivotally connected to the body at a first end and having a roller for engaging the surface of the door at a second end; and an actuator for rotating the door opening arm with respect to the body, from a ready position in which the roller is not forced against the surface of the door, to a door-opened position in which the roller is forced against the surface of the door to open the door. The actuator is remotely and manually operable. The device further includes a support for temporarily and removably bracing the door opening mechanism with respect to the door.