In a cramped nuclear shelter deep beneath the White House, President Bush stared across a spare wooden table and told his national security team, “Get the troops ready.”

Twelve hours after the terrorist strikes, moments after his nationally televised address, Bush was preparing for a war that would transform and define his presidency – with a historic mission, broad new presidential powers and a federal government overhauled to protect against terrorism.

“This is a time for self-defense,” he told his war council. “This is our time.”

The times have also changed Bush personally. Always religious, the president turned more deeply to God. When audience members tell Bush he’s in their prayers, the president gets misty-eyed. He views the prayers as “the ultimate act of love,” Bush told one associate.

A longtime health nut, Bush intensified his exercise regime to burn off stress. Unconsciously, he may have been trying to prove himself disciplined enough to meet the extraordinary challenges, associates say.

Three weeks after the attacks, Bush abruptly asked Condoleezza Rice, his national security adviser, “Are you exercising?”

“Why?” she replied. “Am I especially grumpy or something?”

“You’ve got to get back into it,” Bush said.

The president is said to be more fatalistic about his own safety. Reminded recently that assassination is a constant threat, Bush shrugged his shoulders and said, “It’s not my job to worry about it.”

Associates say he has matured and is more sober-minded – though he is still playful, sometimes silly.

“War changes everyone involved,” said Ron Kaufman, political director for Bush’s father. “It changes not your values, but what you value. People call it maturity, but it’s something deeper than that. You’re dealing with life and death every day.”

After the attacks, friends recall him tearing up as he talked about the attacks in private. Some say it was weeks before he had the time or temperament to start joking again.

“The events, I suppose, have hardened him,” said Joe Allbaugh, director of the Federal Emergency Management Agency and a longtime Bush associate.

Though he has always had swagger, Bush gained confidence in the past year. Critics call it arrogance; they point to his penchant for secrecy and a record of angering allies with unilateral foreign policies.

An effective delegator – critics call him lazy and out of touch – Bush began passing on even more chores after the attacks.

“He had to delegate issues that might have risen to him that now can be managed by others,” White House Chief of Staff Andrew Card said.

Bush now relies on the White House domestic team to implement education reform, a task that would have been an Oval Office issue in peacetime.

Since the moment terrorists struck Sept. 11 – and Card whispered in his ear, “America is under attack” – Bush has seen his presidency transformed.

“It has given the president a special mission, a special opportunity that comes to few presidents,” said Stephen Hess, a presidential analyst who worked in the Eisenhower and Nixon White Houses. “You can compare him to poor Bill Clinton, who hungered for a legacy more than any other but never got an opportunity.”

Unabashedly, White House officials point to America’s greatest wartime presidents – Lincoln and Franklin D. Roosevelt – as well as the Vietnam-scarred Johnson presidency to put Bush’s mission in historical context.

“Every president has an agenda, but they are always subject to the whims of history,” senior adviser Karl Rove said. “The times place demands on them; they give them war, recession and strife – or they give them quietude.”

“This is what history’s given him,” Rove said.