You never cease to amaze me with how shallow your attempt at a logical argument is. You really think a US president has the right to judge impeachment proceedings as invalid?
The constitution doesn't specify how impeachment is initiated and processed.
Congress (house and senate) can absolutely unseat a sitting president whenever they want.
The currently issued subpoenas are valid.
The Nixon impeachment wasn't a criminal proceeding (it wouldn't have been if it happened). Congress does not have the power to charge someone with a crime. The DOJ would have to do that.
Are you capable of an original thought, or do you have to wait for me to have one first so you can repeat it back to me? The Nixon impeachment was based upon the criminal Watergate incident, so yes, it was a criminal proceeding. I gave well sourced documentation of why this is not only unprecedented but outside of their authority. You, you just repeated yourself.
Congress can not indict or convict a someone with of a crime. Just because they are investigating a crime doesn't make it a criminal proceeding.
If Nixon was actually impeached and convicted, he still wouldn't have a criminal record until the DOJ indicted him and he either plead guilty or was found guilty by a trial.
Like the FBI, they can recommend someone get indicted. But they can't actually charge anyone with a crime.