The idea is that there is not a commitment to the death by all opponents---only a few---and to allow the enemy a way out so that you do not force ALL to fight to the death, but to fritter away and splinter. Sun Tzu. Pretty smart guy.
But when there is commitment to death by enough of the other side, you must annihilate them. Their "sacrifice" (or martyrdom) will inspire still others. They must be hunted down and killed or otherwise neutralized *before* than can martyr themselves. In the case of the democrats, they may not really care that much about reelection of individuals, they can always find another schmuck to take the slot.