Answer:
Attempting to fire the Secretary of War, Edwin Stanton.
Step-by-step explanation:
As Johnson and Stanton collided about some south states that were still using black people as slaves, Johnson tried to remove him as secretary, ignoring both the congress and a law that was passed to prevent Stanton to being fired. He impeached the president but, when Johnson was jugded acquitted of any wrongdoing, Stanton voluntarily resigned.