Andrew Nohnson had not broken any laws. He was impeached because he wanted to follow Lincoln’s plan of gentle reunification. The ‘bloody flag’ Republicans wanted punishment. The end result was a neutering Of Johnson and the decades of hatred between north and south that still exists to a degree today.
No Andrew Johnson had broken a law that they enacted specifically for him saying he could not fire someone. He thought it was unconstitutional and fired him anyway. Look it up. It was unconstitutional and was overturned, but at the time that he did it, it was against the law.