As a leader, Willie Stark is uncompromising. He is a commander, not a lecturer or a hero. He is dedicated to a vision of himself that has no regard for morality or ethics. This doesn't make him heartless or immoral, per se, but it does open his character to attacks from his political opponents. And it means that Willie Start does not play by common rules. He plays by his own rules.
To understand the meaning of this character, we should take note of the political achievements of Willie Stark as well as his power-play and political gaming.
Stark got his start in politics by standing up to the corruption in his home county (concerning the contract to build the school house). He also built roads to help farmers get their goods to the market. Finally, Willie’s greatest ambition, the hospital project, is intended to bring free health care to the public of his state. These are all obviously “good” projects. Willie, in light of these projects, is a “man of the people” and a rather great governor.
However, we can say that Willie Stark does become possessive of the constituency he represents. It really is his, after a while, and so is the state. Power, for Willie Stark, is essential to the fulfillment of the vision he has for himself. Nothing will stop him from reaching his goal of becoming a “great man”. This greatness is his vision. It is what sets him apart and allows him to be uncompromising. And part of the vision requires power to be achieved.
This tenacity regarding the achievement of his vision can be construed as corruption because Willie does grease the palms that need to be greased. He blackmails and he threatens to get his way. But it is not a run-of-the-mill corruption that we see in Willie Stark. It is a corruption born out a his two desires - to do good for his people and his state, and to become a great man.