What caused the confrontation between president johnson and congress over reconstruction policies?

(source from https://quizlet.com/36625187/history-1200-ch-15-flash-cards/)

The Tenure of Office Act was enacted, which prohibits the president from removing certain officeholders, including cabinet members, without the consent of the Senate. Johnson considered this unconstitutional and proceeded to do exactly that. In February 1868, he removed Secretary of War Edwin M. Stanton, an ally of the Radicals. He then faced Congress and was impeached. At first the vote was only 35-19, one vote short of 2/3 to impeach him, and then 7 republicans joined democrats in acquitting him, so he was not impeached.

Your answer should be choice b!