"After five-and-a-half years, he thought it might be time to return to private life and this past weekend, I accepted Andy's resignation," Bush said in an announcement made from the Oval Office. "Andy Card has served me and our country in historic times," including the Sept. 11, 2001, attacks, economic ups and downs and the wars in Afghanistan and Iraq, Bush said.
Card, 58, has also made great legislative achievements on issues such as education and Medicare, and he helped confirm two Supreme Court justices, including Chief Justice John Roberts, the president noted.
"In all these challenges, and accomplishments, I have relied on Andy's wise counsel, his calm in crisis, his absolute integrity and his tireless commitment to public service," Bush said with his outgoing chief by his side. "Andy is respected by his colleagues for his humility, his decency and his thoughtfulness. They look at him as a role model and they, like me, will miss him."
The president, who has known Card for 20 years, added: "He's leaving the White House but he'll always be my friend."
Card's resignation, which was not entirely unexpected, is effective April 14.
"I have watched as you have kept your oath to preserve, protect and defend the Constitution," Card said about Bush during remarks he made in the Oval Office on Monday, adding that the White House staff helps the president uphold those values.
"You're a good man, Mr. President, and you do great things."
Although he said that serving the president as chief of staff had been a great honor, "it is a different season and Josh Bolten is the right person for that new season," Card added.
The loyal Bush staffer came to the president recently and suggested that he should step down from the job that he has held from the first day of Bush's presidency, according to one administration official.
Bush decided during a weekend stay at Camp David, Md., to accept Card's resignation and to name Bolten as his replacement.
"This is a tough job and [Card] has been literally by the president's side since the beginning of his presidency," Sen. Jon Kyl, R-Ariz., told FOX News, adding that he has "no idea" why Card resigned.
Bolten, 51, is widely experienced in Washington, both on Capitol Hill as well as at the White House, where he was deputy chief of staff before becoming director of the Office of Management and Budget, where he has spent the last three years. He also worked on Wall Street and for Goldman-Sachs in London.
Bush called Bolten a "creative policy thinker" who is respected by members of both political parties, is a strong advocate of government accountability, is comfortable with responsibility and "knows how to lead."
"No person is better prepared for this important position and I'm honored that Josh has agreed to serve," the president said. "I've got great confidence in my next chief of staff."
Kyl described Bolten as "very smart, accessible, he's very even-handed."
Bolten said Monday that he looks forward to the challenges ahead, including fulfilling the large role Card is leaving behind.
"I'm deeply honored now by the opportunity to succeed Andy Card as White House chief of staff. I said, 'succeed Andy Card, not replace him,' because he cannot be replaced," Bolten said. "His hallmarks of honesty and decency, dedication and courage" not only make him great staff leader, he continued, "but they've also placed him as one of the finest public servants of this generation."
A veteran of the administrations of both President Ronald Reagan and the first President Bush, Card was widely respected by his colleagues in the Bush White House and is known for keeping his cool under pressure. Fellow workers fondly called him "chief."
He may be best known to the public as the aide who calmly walked into a Florida classroom and whispered into Bush's ear that America was under attack on Sept. 11, 2001. When Bush's father, then President George H.W. Bush, got sick at a banquet in Tokyo, aides and security officials ran toward the president. Card ran in the opposite direction, out the door to make sure the motorcade was ready to rush Bush away.
Sen. John Thune, R-S.D., said Card has served this country and the president well and is a well-known "workaholic." He usually arrived at work in the West Wing by around 5:30 a.m. and frequently did not leave until 9 or 10 p.m.
"I think that Andy Card is, if not the longest, one of the longest serving chiefs of staff in any administration," Thune told FOX News. "And that's a very demanding job."
Bolten, he said, is an ideal replacement with his vast experience, "and so, I expect it will be a smooth transition."
"We've got some big challenges ahead and we're looking forward to working with him," Thune added.
"For nearly five and a half years, Andy has turned on the lights in the White House every morning and turned them off every night with unflinching dedication to President Bush and service to the United States," added House Majority Whip Roy Blunt, R-Mo. "I wish him well in this new chapter."
Calling Bolten an "excellent" choice to succeed Card, Senate Majority Leader Bill Frist said Bolten "has proven himself as a dynamic and creative policymaker and a committed public servant. He's a master of the budget and economic issues with a wealth of experience in government."
The Tennessee Republican added: "Andrew Card has provided strong and steady leadership at the White House during some of our nation's most turbulent times and he leaves behind a storied legacy. His presence will be missed but I look forward to working with Josh Bolten as the Senate continues working with the administration to implement policies that keep America strong, free and safe."
At a White House news conference last week, Bush was asked about rumors that a shakeup in the White House staff was in the works. Bush said he was "satisfied with the people I've surrounded myself with."
"I've got a staff of people that have, first of all, placed their country above their self-interests," he said at the time. "These are good, hard- working, decent people. And we've dealt with a lot. We've dealt with a lot. We've dealt with war. We've dealt with recession. We've dealt with scandal. We've dealt with Katrina.
"I mean, they've had a lot on their plate. And I appreciate their performance and their hard work and they've got my confidence," he said. "We've been a remarkably stable administration, and I think that's good for the country."
Change of Course Not Expected
Michael Barone, a FOX News contributor and senior writer with U.S. News and World Report, said that whereas Card tended to give more of the White House line on issues, Bolten is seen by many in Washington as someone who is more frank and may be a better interlocutor with Capitol Hill. Lawmakers may feel more comfortable weighing in on issues with Bolten than they were with Card, he added.
"I don't think we can expect big changes but I think, inside conversationally ... there will be somewhat of a different tone," Barone said.
Some Republican have called for new blood in the White House after what some deem a series of missteps by the administration, including the seemingly blundered response to Hurricane Katrina. Democrats have called the administration incompetent and have taken aim at a variety of staffers, including senior Bush adviser Karl Rove.
"The good news is the administration has finally realized it needs to change its ways, but the problems go far deeper than one staffer," said Sen. Charles Schumer, D-N.Y. "Simply rearranging the deck chairs on the Titanic by replacing Andy Card with Josh Bolten without a dramatic change in policy will not right this ship."
Sen. Trent Lott said he doesn't think Card's resignation constitutes that type of a "shakeup."
"This is not about really shaking up the staff, I think it's about the chief of staff, who has been there such a long period of time, about needing a break," said the Mississippi Republican. "That position chews up people ... I think he just felt it was time for him to get a different life."
While Lott agreed that Bush may need some new people with "stature and gravitas" around him in the White House, "I don't think it means the removal of people who are there."
Even some Democrats said Card wasn't the person they were hoping to leave the White House.
"I have always found Andy Card to be reasonable, professional and a man of his word. If the White House is looking to change course, they picked the wrong person to toss overboard," said Sen. Dick Durbin, D-Ill. "The American people are looking for a new direction from the Bush administration. It remains to be seen whether Josh Bolton can put the White House on the right course."
It's not expected that the conservative Bolten, who is well-liked and respected, will bring about great change to the way the president or White House operates, but some say he may bring about more personnel changes.
"I don't think this rises to the level of a shakeup but it think Josh Bolten would like to see some new people and new ideas brought into the White House so now we'll see if he has the clout to get a real shakeup underway," said Eleanor Clift, a Newsweek columnist and FOX News contributor who noted that this is only a "modest change" given the fact that the "political powerhouse" of Rove is still in place.
"He's going to have great leeway to reshape the White House staff … he is someone known to be the White House staff and indeed the whole administration, needs new blood," added Fred Barnes, executive editor of The Weekly Standard and co-host of FOX News' "The Beltway Boys."
Even if it's moving current staffers to different positions, Barnes said, "shuffling the deck can really create a new energy and new excitement in this administration. You don't want to live out the last few years of your presidency, your second term, just sort of struggle through and leave.
"I think if you change the faces, you can change the subject in Washington," he added.
The Associated Press contributed to this report.