When does a player kill a character to fulfil the instructions on Condemed by the realm (Core set T202) or The Red Wedding (PotS 57)?

Does this happen in the plot phase or is the player oblijed to make a military challenge to attempt to kill the character of their choice?

Capussa said:

It's not like a military challenge is the only way to kill characters in this game. Heck, the military challenge probably kills a lot fewer characters than direct card effects in the long run.

Thanks, the card stating If able has caused confusion amoungst the group I regually play with

The "if able" part is there in case there isn't any valid choice for the opponent you chose (he controls every character or the ones he doesn't control cannot be killed).