The secretary of war under Grant was impeached after he resigned.
But he was acquitted in the Senate trial because a majority didn’t think a it was constitutional.
I’m asking specifically about presidential impeachment. The Constitution is pretty explicit, “When the President of the United States is tried, the Chief Justice shall preside.”
The excuse for impeaching William W. Belknap was that he resigned for the purpose of evading impeachment.
he was not a elected president and federal official .
meaningless comparison .
It was unconstitutional then, and it's unconstitutional now.