Shekhar,
I agree with your answer, but the confusion comes from the answer in Kaplan GMAT Premier 2010 Edition (page 100), it says that "as a general rule, the number of the verb depends on the sense of the sentence. Because unseating a politician is an action taken by the voters as a group, majority acts as a singular collective noun: "The majority wants to unseat."
I noticed that in MGMAT Sentence Correction, we are taught to treat quantity phrases in the same way as SANAM (some, any, none, all, many) pronouns: the noun in the Of-prepositional phrase will indicate whether the verb is singular or plural.
In this case in A majority of the voters, voters is plural, so we should use WANT.
Can someone kindly verify which one is right?