In 1868, the House of Representatives deemed it appropriate to impeach President Andrew Johnson. Johnson, who served as Abraham Lincoln’s Vice-President and assumed the Presidency upon his assassination, was a Democrat from Tennessee, who had opposed secession but went on to thwart Republican plans for Reconstruction. In response, the Republican Congress passed the Tenure of Office Act, which prevented Johnson from removing members of his Cabinet without approval from the Senate; when Johnson defied the new legislation, by firing his Secretary of War, the House voted to impeach the President, though the Senate ultimately chose not to remove him.

As Brenda Wineapple recounts in her new book, “The Impeachers: The Trial of Andrew Johnson and the Dream of a Just Nation,” the impeachment of Johnson has traditionally been seen as an overreach by Congress, with Republican lawmakers privileging partisan considerations over the separation of powers. Wineapple thinks that this argument overlooks House members’ real, stated reasons for impeaching Johnson: that his opposition to basic tenets of Reconstruction, including the enfranchisement of former slaves, and his contempt for Congress, rendered him unfit to be President.

This debate is newly relevant after the release of the Mueller report, with some Democrats arguing that, despite Mueller’s decision not to charge President Trump with obstruction, Trump remains unfit for the office. To discuss how Johnson came to be impeached, I recently spoke by phone with Wineapple. During our conversation, which has been edited for length and clarity, we discussed the similarities between Johnson and Trump, the charges against Johnson, and what history tells us about what impeachment can and cannot accomplish.

You write, “To reduce the impeachment of Andrew Johnson to a mistaken incident in American history, a bad taste in the collective mouth, disagreeable and embarrassing, is to forget the extent to which slavery and thus the very fate of the nation lay behind Johnson’s impeachment.” That is not the version of Johnson’s impeachment that is usually taught. Are you trying to offer a corrective?