The Iraq war was the central issue of Rumsfeld's nearly six-year tenure, and unhappiness with the war was a major element of voter dissatisfaction Tuesday — and the main impetus for his departure. Even some GOP lawmakers became critical of the war's management, and growing numbers of politicians were urging President Bush to replace Rumsfeld.
Mr. Bush said, 63, who has served in a variety of national security jobs under six previous presidents, would be nominated to replace Rumsfeld. Gates, currently the president of Texas A&M University, is a Bush family friend and a member of an independent group studying the way ahead in Iraq.
The White House hopes that replacing Rumsfeld with Gates can help refresh U.S. policy on the deeply unpopular war and perhaps establish a stronger rapport with the new Congress. Rumsfeld had a rocky relationship with many lawmakers.
"Secretary Rumsfeld and I agreed that sometimes it's necessary to have a fresh perspective," Mr. Bush said in the abrupt announcement during a post-election news conference.
Gates is currently a member of the Iraq study group, which is charged with charting a new course in Iraq, CBS News chief White House correspondent Jim Axelrod reports.
"Because our long-term strategic interests and our national and homeland security are at risk, I did not hesitate when the president asked me to return to duty," Gates said.
In a later appearance at the White House with Rumsfeld and Gates at his side, President Bush praised both men, thanked Rumsfeld for his service and predicted that Gates would bring fresh ideas.
"The secretary of defense must be a man of vision who can see threats still over the horizon and prepare our nation to meet them. Bob Gates is the right man to meet both of these critical challenges," the president said.
In brief remarks, Rumsfeld described the Iraq conflict as a "little understood, unfamiliar war" that is "complex for people to comprehend." Upon his return to the Pentagon after appearing with Mr. Bush and Gates, Rumsfeld said it was a good time for him to leave.
"It will be a different Congress, a different environment, moving toward a presidential election and a lot of partisanship, and it struck me that this would be a good thing for everybody," Rumsfeld told reporters.
But underscoring that he would not bow to those pushing for a quick U.S. withdrawal, he also said, "I'd like our troops to come home, too, but I want them to come home with victory."
There was little outward reaction among officials at the Pentagon, beyond surprise at the abrupt announcement.
Asked whether Rumsfeld's departure signaled a new direction in a war that has claimed the lives of more than 2,800 U.S. troops and cost more than $300 billion, Mr. Bush said, "Well, there's certainly going to be new leadership at the Pentagon."
Despite saying that he wanted to work with Democrats on Iraq, at times Mr. Bush seemed as dug in as ever about compromising on his wartime policies, Axelrod reports.
"See, if the goal is success, then we can work together," Mr. Bush said. "If the goal is to get out now regardless, then that's going to be hard to work together."
Voters appeared to be telling politicians that the sooner the war ends the better. Surveys at polling places showed that about six in 10 voters disapproved of the war and only a third believed it had improved long-term security in the United States.
Democrats have long called for Rumsfeld's resignation, reports CBS News correspondent Bob Fuss, but just last week President Bush told reporters that he expected Rumsfeld, 74, to remain until the end of the administration's term. And although Mr. Bush said Wednesday that his decision to replace Rumsfeld was not based on politics, the announcement of a Pentagon shake-up came on the heels of Tuesday's voting.
With his often-combative defense of the war in Iraq, Rumsfeld had been the administration's face of the conflict. He became more of a target — and more politically vulnerable — as the war grew increasingly unpopular at home amid rising violence and with no end in sight.
"I have benefited greatly from criticism, and at no time have I suffered a lack thereof," Rumsfeld said, invoking the words of Winston Churchill.
Gates ran the CIA under the first President Bush during the first Gulf war. He retired from government in 1993.
He joined the CIA in 1966 and is the only agency employee to rise from an entry level job to become director. A native of Kansas, he made a name for himself as an analyst specializing in the former Soviet Union and he served in the intelligence community for more than a quarter century, under six presidents.
Numerous Democrats in Congress had been calling for Rumsfeld's resignation for many months, asserting that his management of the war and of the military had been a resounding failure. Critics also accused Rumsfeld of not fully considering the advice of his generals and of refusing to consider alternative courses of action.
Sen. Carl Levin of Michigan and Rep. Ike Skelton of Missouri — the top Democrats on the Armed Services committees — said the resignation would be a positive step only if accompanied by a change in policy.
"I think it is critical that this change be more than just a different face on the old policy," Skelton said.
Some servicemembers are hopeful for a change. CBS News chief foreign correspondent Lara Logan spoke to commanders on the ground in Iraq.
"Perhaps the most damning reaction I've heard is that this comes three years too late," Logan said.
Rumsfeld has served in the job longer than anyone except Robert McNamara, who became Secretary of Defense during the Kennedy administration and remained until 1968. Rumsfeld is the only person to have served in the job twice; his previous tour was during the Ford administration.
Rumsfeld had twice previously offered his resignation to President Bush — once during the Abu Ghraib prisoner abuse scandal in spring 2004 and again shortly after that. Both times the president refused to let him leave.
Gates took over the CIA as acting director in 1987, when William Casey was terminally ill with cancer. Questions were raised about Gates' knowledge of the Iran-Contra affair, and he withdrew from consideration to take over the CIA permanently. Yet he stayed on as deputy director.
Then-National Security Adviser Brent Scowcroft, who has been a critic of the younger Bush's policies, asked Gates to be his deputy in 1989 during the administration of George Bush's father. The elder President Bush, a former CIA Director himself, asked Gates to run the CIA two years later.
Gates won confirmation, but only after hearings in which he was accused by CIA officials of manipulating intelligence as a senior analyst in the 1980s. Throughout the time period, Gates also became close friends with the Bush family.
"The fact that he is going to that circle, and he has been very reluctant to do that in the past," suggests to me that he is looking to reevaluate Iraq, CBS News chief Washington correspondent Bob Schieffer reports.
Melvin Goodman, a former CIA division chief for Soviet affairs, testified that Gates politicized the intelligence on Iran, Nicaragua, Afghanistan and the Soviet Union. "Gates' role in this activity was to corrupt the process and the ethics of intelligence on all of these issues," Goodman testified.
The Bush administration's use of intelligence on Iraq has been a central theme of criticism from Democrats who say the White House stretched faulty intelligence from U.S. spy agencies to justify invading Iraq in 2003.
Gates has taken a much lower profile since leaving government. He joined corporate boards and wrote a memoir, "From The Shadows: The Ultimate Insider's Story of Five Presidents and How They Won the Cold War." It was published in 1996.
Gates is a close friend of the Bush family, and particularly the first President Bush. He became the president of Texas A&M University in August 2002. The university is home to the presidential library of the elder Mr. Bush.