Several members of Congress had been urging Rumsfeld's resignation before he asserted to the American Legion that opponents displayed the kind of thinking that delayed military action against Adolf Hitler's Nazi Germany.
Rumsfeld said the world faces "a new type of fascism." And he warned against repeating the pre-World War II mistake of appeasement.
Rumsfeld's speech in Salt Lake City Tuesday, in which he also said that administration critics suffered from "moral confusion," prompted angry reactions from Democrats hoping to win back the majority in Congress.
"It is a dangerous business to accuse those who disagree with you of moral and intellectual confusion," said Rep. Ike Skelton of Missouri, the top Democrat on the House Armed Services Committee. "Debate in our democracy is based upon respect, not vilification."
Said House Democratic Leader Nancy Pelosi: "If Mr. Rumsfeld is so concerned with comparisons to World War II, he should explain why our troops have now been fighting in Iraq longer than it took our forces to defeat the Nazis in Europe."
Responding Wednesday, Pentagon press secretary Eric Ruff said, "Facts are facts. As the secretary said in his speech, America and the free world face a gathering threat of challenges from a vicious enemy that is serious, lethal and relentless. There are important lessons from history that we ought to be mindful of as we talk about how we are going to meet the challenges extremist terror organizations present."
In his speech, Rumsfeld said it "was apparent that many have still not learned history's lessons." Aides later said he was not accusing the administration's critics of trying to appease the terrorists but was cautioning against a repeat of errors made in earlier eras.
Nevertheless, Rumsfeld's remarks were seen by many Democrats in Congress as fighting words.
Sen. Jack Reed, a member of the Armed Services Committee, said Rumsfeld has been "substituting sloganing for strategy" and delivered a "calculated political argument" to make people believe that to support a war against terror requires support of the administration's policies.
"I think the analogy is very, very weak," Reed, D-R.I., said of Rumsfeld's comparison of Iraq to World War II.
It is time Rumsfeld "should be departing" the Pentagon, Reed added. Reed, Pelosi and other Democrats have been calling for the defense secretary's resignation for more than a year.
Sen. Charles E. Schumer of New York called Rumsfeld's portrayal of Democrats a "strawman" and said Americans need answers on how to deal with a looming civil war in Iraq.
Also Wednesday, a New York Democratic House candidate accused Rumsfeld of lying about progress in Iraq.
"After 21 months of trying to find something I can agree with Secretary Rumsfeld on, it is true: the American people are being lied to and I totally agree with Secretary Rumsfeld," Eric Massa, a Navy veteran, said in a conference call with reporters.
"What I disagree with is the fact that he's the one doing the lying," he said.
Massa, who is challenging one-term Republican Rep. Randy Kuhl, said he was outraged by Rumsfeld's comments and faulted him for blaming the media for his own misstatements and missteps. said the Bush administration has no effective plan to secure the country.
"This thing has disintegrated," Walz said of Iraq. "On the macro level, there's an absolute failure."
Tracey Schmitt, a spokeswoman for the Republican National Committee, said the Democratic candidates' strategy is to criticize Republican efforts to win the war on terror, while elected Democrats are "committed to a strategy that will weaken our ability to defend America and make us less safe at home and abroad."