As part of a recent CNN special called Black in America much new information came to light about the FBI's surveillance of Martin Luther King Jr., information that should stand as a stark warning of the dangers of allowing one branch of government to engage in surveillance of American citizens without oversight from another.

That is precisely what happened in the 60s under J. Edgar Hoover, who kept up a relentless and obsessive campaign to eavesdrop on King and use anything he found to discredit the civil rights leader, all in blatant violation of the 4th amendment prohibition on unlawful searches. The 4th amendment requires that all searches and surveillance on American citizens be undertaken only after showing probable cause and getting a warrant from a judge, yet the only person who authorized the bugging of King's home and the tapping of his phones was Robert Kennedy, attorney general at the time.

After King delivered his famous "I have a dream" speech in Washington in August 1963, the FBI began to focus enormous institutional attention on him. One FBI memo from just after that speech declared King the "most dangerous and effective Negro leader in the country," while another called for a meeting of department heads to "explore how best to carry on our investigation [of King] to produce the desired results without embarrassment to the Bureau." Left unsaid is any legitimate reason why the FBI should be investigating King at all, a man clearly being surveilled solely because he advocated ideas the government didn't like.

One month after that famous speech, Kennedy approved a request from Hoover to allow the FBI to break into King's home and place recording devices. There doesn't appear to be any concern at all for the legality of the operation; Kennedy's only concern was for the "delicacy of this particular matter" and he wanted to make sure that the agents didn't get caught planting the bugs. The chief law enforcement officer in the nation, sworn to uphold the constitution, had given permission to the FBI to flagrantly break the law and violate the constitution by bugging the home of a man who had broken no laws whatsoever, a man who had done nothing but engage in perfectly legal protest against laws that are universally viewed with disgust today.

The FBI memos do a great deal of bleating about King being a communist, but all their efforts to entrap him turned up not a shred of evidence for that slur. But that wasn't really the point of the investigation. Their real goal was to find anything they could use to discredit or blackmail King. In a couple of instances, their bugs in hotel rooms revealed the kind of private behavior that the government should have no access to at all, including telling off-color jokes and engaging in sexual activities. One can only cringe at J. Edgar Hoover, himself a closet cross-dresser, writing memos calling King a "degenerate."

At one point, the FBI actually sent a letter to King - anonymous, of course - telling him they were going to reveal everything publicly and apparently encouraging him to commit suicide. The letter called King an "evil, abnormal beast" and bluntly declared "you are done." The letter ended by ominously saying, "King, there is only one thing left for you to do. You know what it is ... You better take it before your filthy, abnormal fraudulent self is bared to the nation." That letter was sent in 1964, shortly after it was learned that King was to be awarded the Nobel Peace Prize.

Those who carry water for the Bush administration's equally unconstitutional policy of warrantless wiretapping like to carry on the pretense that anyone who is bothered by such thing is unduly paranoid, a bunch of conspiracy theorists who just need to find something to complain about. "If you haven't done anything wrong, you don't have anything to worry about," is the refrain heard so often. After all, they say, the government is only trying to stop terrorists -- and if you don't want to help them do it, you obviously want the terrorists to win.

But all of this is just so much empty propaganda. This is not a hypothetical. We don't have to invent dystopic fantasies of the government listening in on American citizens who've committed no crimes, they've already done it. We know they've done it. So why in the world would anyone believe that they wouldn't do it again? The constitution is the only safeguard we have in this regard. The founding fathers knew how easy it was for one branch of government to get obsessed with their enemies and use their power to destroy them. They sought to prevent that from happening by creating checks and balances on that power.

The primary check on the surveillance power of the executive branch is the 4th amendment requirement that no search or seizure may take place without a warrant from a member of the judicial branch, and only then upon a showing of probable cause. In the case of foreign intelligence gathering that might involve an American citizen, we have already pared that requirement down to a bare minimum. Under the FISA law, the executive branch can engage in surveillance on an emergency basis and go back and ask the judge for a retroactive warrant within 72 hours.

We've already weakened the probable cause requirement, allowing the executive branch to issue National Security Letters that certify that a given request for surveillance is part of a national security investigation. And we now know that the FBI has abused that authority literally thousands of times over the last few years, according to a Department of Justice report. We've already set up a secret court to hear such warrant requests to insure that no sensitive information will be released, and we've already passed a law that makes it a crime for anyone who is under surveillance to be informed of that fact.

But even these already weakened safeguards are too much for the Bush administration. They insist that the president has the unilateral power to authorize the FBI, the CIA and the NSA to listen in on any phone conversation or intercept any email, even those to or from American citizens, without ever asking for a warrant even from the secret FISA court. No need to meet the probable cause standard, or any other standard, because no one outside of those agencies will ever know who is being surveilled or why. In short, they insist that they have the omnipotent authority claimed by J. Edgar Hoover and Robert Kennedy in the 1960s.

Could they be using that power to do what Hoover and Kennedy did, to dig up dirt on political opponents that can be used to keep them compliant? Does that sound paranoid to you? It shouldn't. Those who ignore history, remember, are doomed to repeat it, and this is a lesson we should have learned long ago. If we allow the government to operate with impunity, to ignore the safeguards set up to protect our liberty, we cannot be surprised when we find that liberty imperiled.

The great jurist Learned Hand famously said: 'Liberty lies in the hearts of men and women; when it dies there, no constitution, no law, no court can save it; no constitution, no court, no law can even do much to help it. While it lies there it needs no constitution, no law, no court to save it.'' It is time for Americans to stand up for liberty and take back the reins of power from those who claim authority that is both unlimited and unchallengeable. If we do not, we will only have ourselves to blame.