A peer opponent's ability to take the fight back

Does a peer threat mean an opponent against whom a force cannot pull its punches or maintain tidy rules of engagement?

The distinction is an enemy's ability to take the fighting back to you and exploit an opening.

The proposed definition focuses on what the opponent can do in return. Japan supplies an example of an enemy able to exploit openings and carry the fighting back to its adversaries. Interventions in the former Yugoslavia offer a different case because the opposing forces could not threaten London or the coalition's air bases in Italy. The comparison concerns the reach of retaliation, rather than a claim that an intervening force must use every weapon available.