Final answer:
The myth of Robert Johnson, the musician, making a deal with the devil stems from the dramatic improvement in his guitar playing skills after a brief absence, which led to speculations and legends within his cultural context. The text provided, however, discusses the pitfalls of Andrew Johnson's presidency and is unrelated to the blues musician's lore.
Step-by-step explanation:
When Robert Johnson returned from a six month absence, people speculated he had "made a deal with the devil" because of his sudden and remarkable proficiency in playing the blues guitar. However, the provided reference text does not relate to this Robert Johnson, a legendary musician, but to Andrew Johnson, the 17th President of the United States, whose reputation suffered during his presidency, particularly due to his disagreements with the Radical Republicans over Reconstruction and his perceived ineptitude and controversial statements.
Instead, the real reason behind the myth surrounding the musician Robert Johnson's supposed deal is rooted in the cultural context of the Mississippi Delta where he lived, and the dramatic improvement in his musical abilities after his disappearance. This myth was compounded by his early death and the mysterious circumstances surrounding his life and talent, leading to a lasting legend in the history of the blues genre.
The referenced text rather discusses President Andrew Johnson's controversial polices and actions during his presidency, including his views on race, his initial agreement with punishing the South post-Civil War, and his deteriorating relationship with Congress which eventually led to his impeachment. Johnson's presidency illustrates the deep divisions in American society during Reconstruction and the challenges of restoring national unity after the Civil War.