The U.S. defense secretary has been criticized over a lack of armored vehicles for U.S. troops in Iraq.
He also came under fire for using a machine to copy his signature onto more than 1,000 condolence letters sent to the families of dead soldiers, rather than signing the messages by hand.
Yesterday, he was once again put on the defensive when a journalist asked him why security measures were not enough to prevent a suicide bomber from entering a crowded U.S. military facility in northern Iraq and detonating an explosive device that left 22 others dead, most of them U.S. soldiers.
Rumsfeld said it was "an enormous challenge" to provide troop protection, and "something that our forces worry about and work on constantly."
"I am truly saddened by the thought that anyone could have the impression that I or others here are doing anything other than working urgently to see that the lives of the fighting men and women are protected and are cared for in every way humanly possible," Rumsfeld said.
U.S. military officials had originally speculated that the 21 December blast in Mosul was the result of a rocket or mortar fired from outside the base.
But yesterday's announcement -- by General Richard Myers, the chairman of the Joint Chiefs of Staff -- that the attack was most likely caused by a suicide bomber has raised fresh doubts. Are U.S. military planners able to provide American troops with sufficient protection? And does the deadly Mosul attack signal a need for a shift in strategy?
Anthony Cordesman is a former intelligence analyst for the Pentagon and U.S. State Department who is now a scholar at the Center for Strategic and International Studies, a Washington-based think tank. He said the Mosul attack, while devastating, is not cause for a change in U.S. military strategy in Iraq.
"We have to put this in context. There are somewhere between 1,600 and 2,500 incidents a month in Iraq. There are going to be cases where the insurgents are much more effective than they are in other cases. And horrifying as this incident is, to put it in further perspective, just a few days earlier, you'd seen in Najaf and Karbala 68 Iraqis killed in those attacks and 175 wounded. This is a reminder of the fact this is a real war. And picking on any one incident as a reason to change strategy is a very dangerous response," Cordesman told RFE/RL.
Other observers say it is time for the United States to make political initiatives -- rather than military operations -- the main priority in Iraq.
The International Crisis Group (ICG), a nongovernmental organization seeking to prevent and resolve deadly conflicts worldwide, on 21 Deember issued a report calling on Washington to shift its strategy and hand more authority to Iraqis. The report says the U.S. military should focus on gaining popular support among Iraqi civilians -- not on eliminating insurgents.
Mark Schneider, the senior vice president of ICG, said Washington's counterinsurgency strategy should be aimed at driving a wedge between the two main elements of the insurgency -- foreign-based extremists and the nationalist Sunnis unhappy with the U.S. presence.
One way to do this, according to Schneider, is to draw more moderate Sunnis into the political process. "What we're basically saying is you at least need to divide them, you need to have a counterinsurgency strategy that takes away those Sunnis who want a new political future, one in which they have a greater opportunity to participate, but one in which they don't see the U.S. dominating," he said.
The United States remains committed to a 30 January date for elections to Iraq's National Assembly. Officials in Washington point to the ballot as a sign of gradual normalization in the country. But continued unrest has raised questions of whether the vote can reasonably be held on schedule, and without major violence.
Daniel Serwer, an expert at the U.S. Institute for Peace, recently returned from a series of conflict-resolution workshops in Iraq. He told RFE/RL that he is not sure whether Iraq is technically capable of proceeding with the vote in January. But he said Iraqis from all ethnic and religious groups are determined to go forward on schedule.
Serwer also emphasized the need for the United States to put greater emphasis on Iraq's political development. "I think the notion of subordinating military strategy to a political strategy isn't quite right," he said. "In any case, it's not exactly the way the United States operates. But I think there's a need for a stronger political pillar. You can ravage Mosul the way you ravaged Fallujah, but it doesn't solve the problem."
But any future efforts by the United States to gain popular support may be hampered by an exodus of foreign companies engaged in reconstruction work.
A Pentagon official yesterday said a major construction company has withdrawn from its contract after a surge of attacks on reconstruction projects. The company, Contrack International, led a coalition of firms working on a $325 million contract to rebuild the country's roads, bridges, and railways.
(RFE/RL correspondent Robert McMahon contributed to this report.)
[For the latest news on Iraq, see RFE/RL's webpage on "The New Iraq".]