DuracellEnergizer said:

The OT Jedi were spiritual warrior monks who served as the guardians of peace and justice in the Old Republic for a thousand generations. The PT Jedi were aloof genetic supermen who served as the enforcers of a corrupt Republic for a thousand years.

I don't think anyone could sum it up any better than this.

At the start of the prequels, the Republic should have been in a golden age. The Jedi should have been almost entirely separate; off on some relatively undeveloped planet being used as a monastery for training and meditation. The only contact between the Jedi and the Republic should have been in the form of occasional moral guidance with respect to "the force."

Having some sort of proxy between the Jedi and the Republic would have been a great role for Anakin. He would have developed close ties within the Republic and a desire to involve the Jedi in political matters. The Jedi would naturally be opposed. Even when it is revealed that there is a Sith lurking in the shadows, the Jedi still avoid political involvement, instead, opting to conduct their own investigation. Anakin would grow frustrated with their lack of "open" involvement, and take matters into his own hands, fighting for the republic and leading their armies into battle.