The comparison made by Senator Dick Durbin, the assistant Democratic leader, last week sparked a firestorm of controversy.
Speaking on the Senate floor, Mr. Durbin, of Illinois, cited an FBI report describing Guantanamo Bay prisoners chained to the floor in the fetal position without food or water and occasionally in extreme temperatures.
"If I read this to you and I did not tell you it was an FBI agent describing what Americans had done to prisoners in their control, you would most certainly believe this must have been done by Nazis or Soviets in their gulags or some mad regime, Pol Pot or others that had no concerned for human beings. Sadly, that is not the case," Mr. Durbin says. "This was the action of Americans in the treatment of their prisoners.
The White House immediately denounced the comments as reprehensible.
Speaking to Mr. Durbin on the Senate floor days later, the chairman of the Senate Armed Services Committee, Senator John Warner of Virginia, demanded his colleague apologize to those who serve in the U.S. military.
"To say that the allegations of a single FBI agent in an unconfirmed, uncorroborated report, give rise to coming to the floor and raising the allegation that whatever persons of the uniformed military, as referred to in that report-albeit an uncorroborated report-are to be equated with those three chapters in world history, is just a most grievous misjudgment on your part and one that I think that is deserving of apologizing to the men and women in uniform," Mr. Warner says.
Senator Warner expressed concern about the impact such comments could have as the United States wages a war on terrorism.
"We have got to be extraordinarily careful in our remarks on the floor of the Senate as they relate to the safety of our people, because this series of statements that you made here, factual references to chapters of history, can be manipulated by other people throughout the world to their advantage, and that is my deep concern," he added.
Senator Durbin responded that his comments had been misinterpreted.
"It is a comparison in relation to the form of interrogation, that an oppressive regime goes too far, that a democracy never reaches that extreme," Mr. Durbin says. "But to say that I am in any way diminishing the horrors, other horrors brought on by these regimes is just plain wrong."
That was not enough for Republican leaders, who joined Senator Warner in demanding an apology. Senate Majority leader Bill Frist issued a statement saying 'Shameful does not begin to describe this heinous slander against our country'.
The Anti-Defamation League also called for an apology.
On Tuesday, Mr. Durbin was forthcoming, his voice filled with emotion.
"I am sorry if anything that I said caused any offense or pain to those who have such bitter memories of the holocaust, the greatest moral tragedy of our time," Mr. Durbin says. "Nothing, nothing, should ever be said to demean or diminish that moral tragedy. I am also sorry if anything I said in any way cast a negative light on our fine men and women in the military."
Senator John McCain praised Mr. Durbin for doing what he called the courageous thing, and he joined Democrats in expressing hope the issue could be laid to rest.