[t]o the victor belong the spoils of the enemy.
based on this quotation, william marcy could best be described as a jackson
critic.
rival.
opponent.
supporter

He would be a supporter. That is because the quote means that if you win the presidency, everything around country running belongs to you, so you're allowed to fire everyone and place your own people. Of course, the system doesn't exist anymore because it's a form of corruption and a merit system was implemented instead of it.