The march circled the White House grounds, but the man the protesters wanted to persuade was out of town. Bush was in Colorado and Texas to oversee the Hurricane Rita recovery efforts.
But President Bush knew the protesters were coming. In Washington on 22 September he anticipated the march, acknowledging the sincerity of the demonstrators, but voicing his disagreement with their demand that he end the war: "Listen, there are differences of opinion about the way forward [in Iraq]. I understand that. Some Americans want us to withdraw our troops so that we can escape the violence. I recognize their good intentions, but their position is wrong. Withdrawing our troops would make the world more dangerous and make America less safe."
For the most part, the protesters seemed cheerful as they passed the presidential mansion. But when interviewed, they expressed anger at Bush and frustration over the toll the war is taking.
One was Mary Musselman, a middle-aged obstetrician-gynecologist from the Washington suburb of Bethesda. She told RFE/RL that as a Christian, she finds Bush's reasons for going to war unacceptable.
Musselman said Bush, who is also a Christian, flouts the words of Jesus in Christian scripture: "Blessed are the peacemakers." And she pointed to the casualties -- nearly 2,000 Americans have died in Iraq, and as many as 20,000 Iraqis, she said.
"There have been so many lives lost," she said. "As a physician, I think that it's -- the number of Iraqi lives we've lost, the number of American lives we've lost, the number of American boys injured and women [soldiers] injured -- this is, this is awful."
Musselman warned that Americans will "be judged by the way we treat others." Another demonstrator elaborated on that theme. He is Michael Durr, an elderly Washington physician.
Durr told RFE/RL that he worries about America's standing in the world and the retribution it may face because of the war, which he called a debacle: "It's [the war has] resulted in the entire world looking on America as murderers. I mean, it's turned the world against us. I think our chance of terrorism against us has increased enormously."
Durr said it's time for all Americans who oppose the war to take to the streets to show Bush they want the war to end.
Today's march in some ways resembled the demonstrations against the Vietnam war during the 1960s and early 1970s. But those protests were attended primarily by students and other young people. This event included people of all ages and backgrounds.
Still, youth was well represented. Sascha Bollag -- a college student from North Carolina -- marched with several family members, including his mother.
Bollag told RFE/RL that he does not believe Bush decided to go to war because he believed that Iraqi President Saddam Hussein, now deposed, had an arsenal of illegal weapons. Bollag sees something more sinister.
"Because this war wasn't fought to help any people. It was fought for strategic control of the Middle East and also for oil interests," he said.
The march in Washington wasn't the only antiwar event. An estimated 10,000 people rallied in London in opposition to the war. Meanwhile, supporters of Bush's Iraq policies plan a counterdemonstration in Washington today.