You expect to be judged fairly on accomplishments and/or failures in your particular sphere of responsibility? That's not politics -- not now, and not then. As marshal, you're the king's main adviser. His subjects can't blame the king, so everything they feel like blaming on someone, they'll blame on you -- military defeats, banditry, the cows giving sour milk, solar eclipses, you name it.
I'm not quite sure how you're seeing your controversy shoot up to 100 in two days, though. NPC marshals can usually hang on to the position for a couple of weeks.
That being said, I should introduce some rewards, and give a small deduction for damage inflicted on the enemy.