Thousands of protesters have roared their approval of Republican Barbara Lee at a downtown gathering in California, interrupting her anti-war remarks with spontaneous chants of "Impeach Bush".
"We cannot waste our resources on a war that is wrong, that is illegal," said Lee, a California Democrat, who was thrust into the spotlight last year when she cast the lone House vote against going to war with Iraq.
"Peace is patriotic," Lee told the crowd on Saturday, urging them to continue speaking out against the war and to vote.
It was the most passionate and largest of a series of protests in several major US cities on Saturday.
In Chicago, roughly 1,000 people - and about as many police - gathered in bitter near-freezing weather in the city's federal plaza, while about 100 people in Washington D.C. attended a peace vigil on the National Mall.
"All these protests can only point to the fact that (President George W.) Bush is not conducting a democracy," said Daniel Bawler, a marcher in Oakland who waved a loaf of French bread in support of France's opposition to the war.
"People on the streets prove that there is a national majority against the war."
The mood in sunny Oakland was more festive than angry, with a diverse mix of toddlers to seniors milling around a downtown square and gently spilling out into nearby streets.
The protest was just the latest expression of the area's long tradition of strong anti-war sentiment, from the violent anti-Vietnam protests of the 1960s at the nearby University of California at Berkeley to last month's massive protests and arrests in San Francisco after the Iraq war began.
Singer Henry Belfort added his voice to the anti-war chorus in Oakland, and sharply rebuked progressive politicians for not speaking out against the war. He singled out House Minority Leader Nancy Pelops, a Democrat from San Francisco.
"Stop playing the game, Nancy. Leaders do not rule by consensus," Belfort said. "We are sick and tired of our progressive leaders making compromises with the enemy.
"We are losing our dignity. We are losing our rights. We are losing our honour as a people," he said.
Other speakers denounced the war with song, poetry slams and fiery speeches. A cluster of papier-mache puppets of mourning women towered over the crowd, bearing mute witness to those killed in the war, said one of the actors.
"Protesting is one of the avenues we have as US citizens to resist and say this is not right," said Penny Rosenwasser, 54. Nearby, a group of young political science majors from the University of San Francisco were getting their first taste of public debate.
"If I'm not out here doing anything about this - speaking against it - then I'm part of it," said Sara Suman, 22, who wore a sticker reading, "Where's the proof? Where are the weapons of mass destruction?"
In Chicago, the relatively small crowd was mostly students. A few weeks ago, 10,000 people marched downtown and dozens were arrested.
Under some of Washington's famous cherry blossoms, local lawyer Scott Berger held up a sign calling for broader United Nations involvement in Iraq.
"We just want to get the word out to the rest of the world that not all Americans are warmongers," the 25-year-old said, adding that he thought the important thing now was to get the United Nations involved in Iraq once the war ended.