Since a president will only be impeached if they do something unconstitutional, I believe that impeachment of a president would be justified according to the constitution. Andrew Johnson was the first president to be impeached, along with Bill Clinton and Richard Nixon. The reason why he was impeached was that he violated the Tenure of Office Act and tried to replace secretary of war Edwin Stanton with Major Lorenzo Thomas. The Tenure of Office act was designed specifically to protect the secretary of war, and by Johnson removing Stanton from office, that completely violated the law, and congress felt it was best to impeach Johnson since his actions were unconstitutional.
Hope this helps
