Question

why did the house of representatives impeach andrew johnson?
the president refused to follow lincoln’s reconstruction plan.
the president violated the tenure of office act.
congress wanted to test the fifteenth amendment.
the supreme court supported separation of powers.

Explanation:

Andrew Johnson was impeached by the House in 1868 primarily because he removed Edwin Stanton, the Secretary of War, without Senate approval, which violated the Tenure of Office Act. This act was designed to restrict presidential power over cabinet appointments during Reconstruction. The other options are incorrect: Johnson implemented his own Reconstruction plan (not Lincoln's, but that was not the impeachment cause); the 15th Amendment was ratified later; and the Supreme Court did not drive the impeachment over separation of powers.

Answer:

The president violated the Tenure of Office Act.