When two players are fighting a warden, the warden will only attack one of them.

A warden could be chasing the target player whilst another player attacks it from behind. The warden will never turn around and switch to the other player.

If a player attacks a warden that is fighting any other entity, however, like an iron golem for example, the warden will turn around and attack the player, but will never switch back to the iron golem, even if it damages the warden.