"The President… Shall have Power to grant Reprieves and Pardons for Offences against the United States, except in Cases of Impeachment."
There's only one exception to pardons: impeachment. There's no exception that says "and also if the impeachment was not yours".
So it's a fragrant violation of the US Constitution.
Read more: https://fordnews.org/how-did-ford-pardon-nixon-when-the-us-constitution-says.html
