Use the quotation to answer the following question: "When Andrew Johnson took upon himself the duties of his high office he swore to obey the Constitution and take care that the laws be faithfully executed. That, indeed, is and has always been the chief duty of the President of the United States. The duties of legislation and adjudicating [making a judgment on the laws of his couniry fall in no way to his lot. To obey the commands of sovereign power of the nation, and to see that others should obey them, was his whole duty-a duty which he could not escape, and any attempt to do so would be in direct violation of his official oath..." - Thaddeus Stevens, Closing Remarks in the Impeachment Trial of Andrew Johnson, 1868. According to the quotation, why does Stevens believe that Johnson should be removed from office?