What law did Johnson violate when he was president?

During his presidency, Andrew Johnson violated the Tenure of Office Act, which restricted the president's power to remove certain officeholders without the Senate's approval. In 1868, he dismissed Edwin M. Stanton, the Secretary of War, and attempted to replace him, leading to his impeachment by the House of Representatives. Although he was acquitted by the Senate and remained in office, his actions were a significant factor in the constitutional conflict between the presidency and Congress during Reconstruction.