[This post is excerpted from the new book, National Treasure: How the Declaration of Independence Made America (Avid Reader Press/Simon & Schuster).] Partisanship has plagued American society since before Independence. John Adams notably claimed that at the time of the Revolution, "one full third were averse to the Revolution," one-third in favor, and a final third swinging between the other two.[i] Yet the idealism that inspired the main voices…