Question

Andrew Johnson was impeached by Congress when he

Answer 1

He violated the Tenure of Office Act. Without consulting the Senate, he dismissed his secretary of war, Edwin Stanton.

Answer 2

I believe the answer is: tried to fire his secretary of war in violation of the tenure of office act

At that time, Edwin stanton was his secretary of war. Secretary of war had the power to oversaw the demobilization of us army from confederates states. At that time, Andrew Johnson had a conflict with stanton because stanton believe that Johnson was too lenient toward the ex-confederates.