"Assess Machiavelli'; Governing activities of politicians - Thesis review

"Assess Machiavelli's claim that there is not a separate moral sphere governing the activities of politicians. In your well-supported opinion, is Machiavelli right about this? Be sure to thoroughly explain why Machiavelli's position differs from most common conceptions of the way that political actions can be morally evaluated"

Thesis Statement: In The Prince Machiavelli correctly argues, in contrast to other political thinkers, it is impossible for one to be virtuous and an effective leader simultaneously. The nature of politics requires a leader to make morally ambiguous, if necessary, choices in order to stay in power and to remain an effective leader.

I would change your last sentence to...
"The nature of politics requires a leader, if necessary, to make morally ambiguous choice in order to stay in power and to remain an effective leader"

Also, is "The Prince Machiavelli" a book or are you merely talking about Machiavelli?