One who held the title of Imperator was not above the law, an Imperator, was the law.
In many ways this was a practical and workable solution. The Romans believed that a governor, or commander in the field, often months away from any contact with the Senate or Rome needed the authority to do as he saw fit rather than asking for legal rulings at every step of the way. If there was an insurrection, that needed to be put down, by any means neccessary. If a property confiscation took place in the course of that action, the confiscator needed to be secure in position and not be forced to go back and forth to Rome constantly to defend those actions in court.
Thing was, when the job was over, so was the Imperium. Once the title and the position were finished, all legal bets were off. In his novel, titled "Imperium", Robert Harris tells about Marcus Tullius Cicero's prosecution of Varrus after his term as Governor of Sicily. Varrus was, by all contemporary accounts, a vicious and rapacious thug who raped, robbed and plundered his way through one of the richest provinces in the Roman Sphere. While he held the imperium, he was immune from prosecution of any kind, civil or criminal. When his term ended and he returned to Rome, all bets were off. What began as a civil suit became instead and indictment of the Senatorial class who viewed the world as their own personal playground where they could, with Imperium, indulge what ever depravities crossed their minds. Cicero tried to put a stop to that by holding men accountable for the actions they made. It worked, at least, it worked that one time.
Just like when Nixon was driven from office, all the while claiming his own type of imperium (interview with David Frost, 1974, "If the President orders it, that makes it legal.) The Romans who were on the greasy end of the retribution stick chose to learn their own lessons from the legal system of Imperium.
Many of the worst offenders simply chose to remain abroad. They would take their term of Imperium, loot blind what ever was in front of them, then retire to the eastern provinces of Cappodocia, Macedonia, Egypt, or some other oriental province where money bought luxury and ease.
One holder of Imperium, was Julius Caesar. While pro-consular Military Governor of Gaul, he unilaterally began the Gallic wars. He ordered his legions into action without approval or authority from the senate, and he kept them in the fields until he was stopped by the twin barriers of the Rhine and German resistence. He knew that he had started the war entirely to gain money. The commanding general's share of the spoils in Roman law was huge. He had the largest share of any property or treasures looted, and he had the sole ownership of all captives sold into slavery. Ceasar took on his mantle of Governor mostly broke from his runs for office, he was heavily mortgaged and deeply in cash debt, mostly to Crassus. Caesar was of noble lineage, some of the most noble of Roman Nobles, a direct descendant of both Aeneus and of Venus. Thing was, he was worse than broke, he was in deep debt.
Ten years in Gaul, and Caesar wanted to return to Rome as the richest man in the Empire (and Rome was, by this time a Republic by reputation only), except of course, Crassus. The big problem that he was was that in order to enter Rome itself, he had to lay down his Imperium. Caesar knew that if he did that, decades of lawsuits and criminal prosecutions would ensue. At best, after years of legal wrangling he would be financially ruined and have to return to the status of very noble and very broke, or at worst, banishment, expulsion, and poverty abroad as an exile. Caesar and his legal team came up with all manner of twistings and inventive interpretations of Roman Law, he would run, in absentia, for Consul, or other high office that carried its own Imperium, although the requirement for candidates to stand for office in person would have to be waived. When all of his twistings and turnings of the laws upon their very heads failed, Caesar, still with his Imperium, simply used that very power to break yet another Roman Law. His crossing of the boundary at the Rubicon set off a bitter and bloody civil war. His main goal, throughout his tenure as "Dictator" and then "Dictator for Life" was mainly about avoiding prosecutions for crimes he knew that he had committed. He wanted to avoid a reckoning and judgement. He did. Caesar won, and the Roman Republic was never again anything close to that. It became, instead, under Caesar's heir Octavian, a hereditary monarchy.
President Bush, and his advisors have been claiming their own version of roman Imperium. They have claimed that we are a nation of powerful men, unanswerable to either the people through Congress, the laws through the courts, or simple human decency. They have overturned two hundred and fifty years of checks and balances. They have conducted policy meetings in secret where maps of foriegn countries were spread out on the table and various oil companies were allowed to divvy up the promised loot like a christmas pie. They have then began wars on whims to deliver those promised spoils. They have, worst of all, against the laws of this nation, against the laws of all nations, and against simple human decency instituted a regime that has detained human beings without charges or legal recourse, many of them innocent, they have tortured "confessions" out of those innocents and so perverted any concept of right, truth, and justice that there may never be any accounting or reckoning ever possible. Jose Padilla, Khalid Mohammed, and other victims of the torture regime have been driven to the point of clinical insanity by their treatment. They are so far gone that they have lost the ability to be reliable eyewitnesses to their own lives.
Through this all, Bush and his minions are claiming "Imperium" and saying that they are above, immune, and far beyond all accountings or investigations. By demanding that immunity be granted retroactively in their offenses against the fourth amendment they have admitted that they knowingly broke the law of our land for years. Otherwise, they would not have needed that protection. Hopefully there are courts left in this country that remember the opinion brought down by John Marshall in Marbury vs. Madison which held that Congress cannot simply vote to ignore the Constitution without the cumbersome process involved with amending the Constitution first.
Like the natural result of a system of "Imperium" is someone like Caesar simply using it to seize full and total hereditary power, the swift, and always certain result of an American "Imperium" will be law breaking thugs listening to our communications without cause or warrant or oversight of any kind, snatching people off the the streets both here in our country and abroad, holding them without charge, or indictment, torturing them and then putting them on trial for their very lives using the fruits of the dungeon for evidence.
That this long list of crimes and abuses happened almost from the instant the behaviors began shows the dangers that our founders thought they had protected us against.
It may well be, that as I have said, and now echoed by legal scholars (not old and tired jingle whores, but law professors and shit like Glenn Greenwald and Jonathon Turley) are now saying, like I have said, that our own system of laws and courts might have been too debased and perverted by the rampant lawlessness of recent years and that the International Courts might have to be brought in.
Bring them in I say. I would rather live under foreign laws that the perverse twistings of Authoritarian Gangsters. I am tired of only being able to pretend to my freedoms.