The announced departure of the long-serving U.S. Defense Secretary, Donald Rumsfeld, has started a period of transition at his department, and in U.S. defense policy, particularly toward Iraq.

Donald Rumsfeld speaks at Kansas State University, Nov. 9, 2006

In recent months, a growing number of commentators and members of Congress have been calling for a change in the U.S. strategy in Iraq. During the congressional election campaign, President Bush insisted he would "stay the course," and accused his opponents in the Democratic Party of wanting to "cut and run." But late in the campaign, even the president had to abandon that rhetoric, as it became clear from the surging violence in Iraq that some changes were needed.

The evolution in his thinking came to a climax in a series of meetings during the last week or so, and peaked with his announcement on Wednesday. "Now after a series of thoughtful conversations, Secretary Rumsfeld and I agreed that the timing is right for new leadership at the Pentagon," Mr. Bush said.

The president announced he will nominate former CIA director Robert Gates as that new leader at the Pentagon. Gates was also a member of the commission that has just finished studying U.S. Iraq policy, and that will soon make its recommendations. Analyst Lawrence Korb of the Center for Defense Information says Gates' selection signals that the president is ready to adopt some of the commission's ideas.

"Bob Gates, a year ago, turned down the job of the director of National Intelligence. My feeling is the reason he turned it down is he did not think there were going to be any changes. And he would not have taken (this job) this time unless he felt he could make a difference," he said.

No one knows exactly what the Iraq commission will recommend. Lawrence Korb and other analysts say there is not a lot of room for maneuver short of abandoning the strategic goals of bringing democracy and stability to Iraq. No one expects that. But he says the commission is expected to recommend an acceleration of the handover of responsibility to the Iraqi government, and a substantial reduction of U.S. forces in Iraq starting next year.

"What that will do is basically send a signal to the Iraqis that they've got to make the painful political compromises necessary to create an Iraq the people are willing to support and fight and die for," he said.

From left: Donald Rumsfeld, George Bush and Robert Gates

Announcing the change at Defense, President Bush said he wanted a "fresh perspective" and "new ideas" at what he called "a critical period" in the war on terror. Secretary Rumsfeld himself indicated in an appearance Thursday that tactical and perhaps broader changes are on the way in U.S. policy toward Iraq. "I don't have any doubt but that the president, working with the commanders and the new secretary will continue to make adjustments, and that, if we have the perseverance and the resolve, we will end up seeing the Iraqi people, ultimately, take control of their country," he said.

Speaking at the White House on Wednesday, nominee Robert Gates outlined what he sees as the stakes as he tries to salvage the U.S. mission in Iraq. "The United States is at war, in Iraq and Afghanistan. We're fighting against terrorism worldwide. And we face other serious challenges to peace and our security. I believe the outcome of these conflicts will shape our world for decades to come," he said.

Analyst Mackenzie Eaglen of the Heritage Foundation says Gates may be well positioned to take on the challenges he will face if he is confirmed by the Senate as defense secretary. She notes his experience running the CIA, and also the fact that he started at an entry-level job at the agency. "He sort of rose through the ranks at the CIA, from (being) a bureaucrat to running it. And I think that's a useful perspective to have. You also have to understand the people below you, their challenges in operationally fulfilling the tasks you've assigned to them strategically. And I think that is useful," he said.

Still, Eaglen says Gates will have some work to do to replace Rumsfeld, who she says has a "cult of personality" that has permeated the department.

Here at the Pentagon, career staff members were wondering Thursday what the future will hold. But spokesman Bryan Whitman cautioned reporters not to make too much of the departure of Secretary Rumsfeld, even though he has been such a strong presence in the department for the last six years. "We know that the work of this department transcends any of the people or the personalities of the leadership of the department," he said.

President Bush indicated on Wednesday that Secretary Rumsfeld will serve at least until the end of the year, when he will become the longest-serving defense secretary in U.S. history. But the spokesman, Bryan Whitman, says the knowledge that the secretary is leaving will not create any power vacuum. He says the secretary will continue to carry out all his duties, and make decisions as necessary, and that although it may be an emotional time for some staff members, they will continue to do their jobs, too.

"You can't just check all your feelings at the door, but you have to, as part of a great institution like this, understand that the work of this department must go on, that we cannot afford while we have forces in the field that are fighting this nation's wars to miss a heartbeat. And we're not going to miss a heartbeat, is what I'm telling you. Secretary Rumsfeld would want it that way. He would insist on it that way. And we're going to make sure that it happens that way," he said.

Once the new defense secretary takes office, he is expected to implement some new policies, but President Bush's strategic goals in Iraq and on the broader war on terrorism are not expected to change. In his appearance Thursday, Secretary Rumsfeld said this is "a defining moment in American history." And he said "history will judge whether" this generation did all it could to defeat what he called "a vicious, extremist enemy" that threatens America's security, freedom and way of life.