Work to become president of the US during WW2 and finish the job by taking out Russia and China after Japan/Germany have fallen before anyone else develops nukes. The world is now your oyster.
Edit: Meanwhile, disband the federal bureaucracy and kick out all the minorities.
How much more would an expanded Marshall plan to rebuild Russia and China cost?
How easy would it be for America and Allies to hold/occupy/rebuild Russia and other countries like Poland, plus China etc?