It seems like perhaps that power has been considerably weakened if the President is literally allowed to assassinate political rivals (as is mentioned in the dissent). You might vote not to impeach in fear, similar to jury intimidation. Hell, why even wait, what’s to prevent a President from going for it before the vote even happens? I find it hard to believe that this was meant to be a component of the impeachment process by the founders. To make it more exciting, I guess?