I disagree. What you are saying is that a President can direct his minions to break the law in any way imaginable, but this criminality can only be addressed by means of impeachment, something obviously impossible if his party controls Congress.
Then even if the people revolt and hand control of Congress and the Presidency back to the other party, nobody in the previous administration can be held responsible for criminal acts.
I agree with your characterization of this investigation as politically motivated, I just am worried by the idea that all members of an administration acquire a get out of jail free card on leaving office.
My personal opinion is that the Constitution says nothing about government officials being above the law and not liable to indictment, conviction and punishment for criminal acts.
What you continue to fail to realize or acknowledge is that this WAS investigated. Prosecutorial discretion was exercised, and it was decided that indictments would not be sought. Who has oversight authority of the Department of Justice? The Legislative branch. The Democrats had control of congress in 2006, almost 9 months after a decision was made not to prosecute. Did they press the issue then, did they hold hearings? Nope.
In a nutshell, the executive branch upheld their obligations to enforce US law, and the legislative branch, in their oversight capacity, decided that there wasn't any "there there" with respect to criminality by either the people who authored the relevant legal opinions, or the people who executed the policies based on those opinions.
Now, we have a change of administration, and this new administration wants a second bite of the prosecutorial apple. It's completely counter to every principle of American jurisprudence in which I'm familiar. It may be the most blatant politicization of policy decisions by a prior administration. It's a chilling precedent, not just on our contemporary national defense and security, but it's also a game changer for political prosecution in future administrations. It's horrible.