Majumdar's book is the easiest book available in the market, don't be confused just make a frame in your mind of district, state and national level and then thoroughly study the services of 3 presidents i.e. Theodore Roosevelt, William H. Taft and Wilson. You would find it more easy this way, for removing confusion read as many time as you could, changing books would bring more confusion.

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"Success is not final, failure is not fatal; it is the courage to continue that counts" (Winston Churchill)