President Bush, in a televised address last night, called the war in Iraq "a struggle for civilization" that Americans should "put aside our differences" to win, capping a day of hushed remembrances, tolling bells and wailing bagpipes on the fifth anniversary of the Sept. 11 attacks.
After a daylong tour that took him to the sites in New York's financial district, rural Pennsylvania and Northern Virginia where airplanes-turned-bombs struck that day, Bush said the war would "set the course for this new century."
"If we do not defeat these enemies now," he said, "we will leave our children to face a Middle East overrun by terrorist states and radical dictators armed with nuclear weapons."
The president's words were designed to place him above the partisan fray for the somber occasion and help rekindle the sense of unity that followed the attacks. But they were also part of an election-year effort to reframe the bitterly partisan debate over the war in Iraq, which Bush linked directly to Sept. 11.
Contrasts abounded, five years after the terrorist strikes: from the streaks of gray that now dominate Bush's hair, to the reserved demeanor of a leader who once stood atop a pile of World Trade Center rubble with a bullhorn and boldly promised - in a seminal moment of his presidency - to avenge the strikes.
Bush stayed quiet and grim-faced through a series of heart-wrenching ceremonies, often with head bowed, returning to the White House to deliver a prime-time speech that lasted just over 16 minutes and summed up his argument that invading Iraq was an essential response to 9/11.
"Whatever mistakes have been made in Iraq, the worst mistake would be to think that if we pulled out, the terrorists would leave us alone," he said in one of only a handful of prime-time Oval Office addresses of his presidency. "If we yield Iraq to men like bin Laden, our enemies will be emboldened. They will gain a new safe haven, and they will use Iraq's resources to fuel their extremist movement."
Bush said his response to those who ask "why we are in Iraq when Saddam Hussein was not responsible for the 9/11 attacks" is that Hussein's regime "posed a risk that the world could not afford to take" after the 2001 terrorist strikes.
Bush's carefully planned day of prayer and comforting mourners was a brief respite from the bitter feelings that have come to be associated with the aftermath of Sept. 11. Democrats hope to use discontent over the war and Bush's leadership to defeat Republican candidates this fall.
Vice President Dick Cheney delivered the day's hardest-edged defense of Bush's policies, repeating his earlier suggestion that war critics would surrender in the face of grave threats.
"We have no intention of ignoring or appeasing history's latest gang of fanatics trying to murder their way to power," Cheney said after he observed a moment of silence at the Pentagon. His tone echoed his remark, in a weekend TV interview, that any suggestion that U.S. troops should withdraw from Iraq "validates the strategy of the terrorists."
Sen. Edward M. Kennedy, a Massachusetts Democrat, blasted Bush for his remarks, saying the president "should be ashamed for using a national day of mourning to commandeer the airways" with a speech defending the Iraq war.
Such confrontational words were largely absent from most public statements yesterday.
"We had an astonishing moment of unity in America and around the world," former President Bill Clinton said.
At the same time, former Clinton aides unleashed a barrage of new criticism disputing an ABC docudrama about 9/11, which the network interrupted last night for Bush's speech.
The program showed Clinton's administration missing or botching opportunities to capture bin Laden before he could strike the United States - an account that Clinton associates called defamatory and misleading.
Yesterday's remembrances were punctuated by flashes of the frayed nerves that have become almost commonplace. Authorities diverted a flight bound for San Francisco after finding an unclaimed wireless e-mail device on board. New York's Penn Station was briefly evacuated after someone spotted a suspicious duffel bag, which turned out to be filled with trash.
Thomas H. Kean and Lee H. Hamilton, leaders of the bipartisan 9/11 Commission, faulted the government for failing to implement many of their recommendations for bolstering the nation's defenses.
Sen. John McCain, an Arizona Republican, said that despite lingering vulnerabilities at the nation's ports and rails, "we are safer, and we should be pleased about that. But I hope we don't relax," he told Fox News.
"Today is not only a remembrance, but it's also a reminder," McCain said.
Around the country the grim unfolding of the attacks was marked with quiet moments.
At Ground Zero, there were two silent pauses at 9:59 a.m. and 10:29 a.m., the times when the North and South towers of the World Trade Center collapsed.
At the Pentagon, Defense Secretary Donald H. Rumsfeld appeared emotional as he reflected on his experience five years before. "I remember working our way through that long, tragic day," he said.
Congressional leaders gathered at the foot of the Capitol in the early evening in a scripted ceremony meant to reprise the impromptu moment five years ago when they met and sang "God Bless America" in a rare show of bipartisanship that quickly dissolved into partisan wrangling.
"We are not fully safe, and we are not fully healed," said Rep. Nancy Pelosi of California, the Democratic leader. "It's important for us to come together."
Security screeners wearing "We will never forget" wristbands and passengers who had lined up to be checked at Boston's Logan Airport, where two of the ill-fated flights originated, paused to acknowledge the attacks. In Akron, Ohio, firetrucks sounded their sirens for 30 seconds to mark the moment each tower imploded.
Bush began the day at a breakfast with first responders at "Fort Pitt," the Lower East Side fire station that housed some of the first to arrive at Ground Zero. He and first lady Laura Bush bowed their heads for moments of silence at 8:46 a.m. and 9:03 a.m., to mark the times when passenger jets slammed into the two towers of the World Trade Center - the first jolts in a day of horror that ultimately killed 2,973.
The president next traveled to the Shanksville, Pa., field where an airliner headed toward Washington instead crashed to the ground. Under gray skies and a sharp drizzle, Bush participated in a brief wreath-laying and prayer service there, lingering for more than 20 minutes afterward to greet family members of the victims.
At times, the mourners seemed to be comforting Bush rather than the other way around, as the president moved painstakingly down a line of 9/11 relatives - receiving hugs, pats on the back and rubs on the arm as frequently as he dispensed them.
Later, in front of the rebuilt western wall of the Pentagon, Bush attended another wreath-laying and fought back tears as he embraced victims' relatives.
Makeshift memorials at each site adorned the emptiness that marked the disasters - two flower-strewn reflecting pools where the World Trade Center towers stood; bales of hay piled with bouquets in the Shanksville field where United Flight 93 crashed; a blackened piece of limestone stamped with the fateful date on the west side of the Pentagon.
"Winning this war will require the determined efforts of a unified country. And we must put aside our differences and work together to meet the test that history has given us," Bush said in an address his aides said was designed as apolitical.
There were hints, however, of the divisions over his policies that have helped degrade the president's stature and are providing a vicious undercurrent to the midterm elections.
In a letter to supporters circulated by e-mail, Howard Dean, the Democratic Party chairman, wrote that "the dangers we face know no political party."
email@example.comThe Associated Press contributed to this article.