Andrew Johnson was impeached, but not convicted, because

Responses
A he resigned as President before the Senate could vote.he resigned as President before the Senate could vote.
B the Civil War came to an end with the Union victory over the Confederates.the Civil War came to an end with the Union victory over the Confederates.
C Senate Democrats filibustered in order to prevent a vote from taking place.Senate Democrats filibustered in order to prevent a vote from taking place.
D a few Republicans voted "not guilty" to stop a possible imbalance in the three branches.

A he resigned as President before the Senate could vote.