Jelaskan Sumber primer dari Newton D. Baker

Baker, Newton D. Frontiers of freedom (1918) online

Palmer, Frederick. Newton D. Baker: America at war, based on the personal papers of the secretary of war in the world war; his correspondence with the President and important leaders at home and aboard; the confidential cablegrams between the War departmant and headquarters in France; the minutes of the War industries board, and other first-hand material (Dodd, Meade & Company, 1931)