Washington ? Democrats relentlessly assailed President Bush’s policy in Iraq as a catastrophic failure Tuesday as the House plunged into momentous debate on a war that has lost public support and cost more than 3,100 U.S. troops their lives.

“No more blank checks,” declared Speaker Nancy Pelosi.

“This battle is the most visible part of a global war” against terrorists, countered the Republican leader, Rep. John Boehner, hoping to limit GOP defections on what loomed as an extraordinary wartime rebuke to the commander in chief. “If we leave, they will follow us home. It’s that simple.”

The Democratic leadership set aside most of the week for the historic debate, expected to culminate in a vote Friday on a bare-bones, nonbinding resolution that “disapproves of the decision of President George W. Bush : to deploy more than 20,000 additional United States combat troops to Iraq.”

The 95-word measure adds that “Congress and the American people will continue to support and protect the members of the United States armed forces who are serving or who have served bravely and honorably in Iraq.”

The debate was Congress’ first on Iraq since Democrats gained control of the House and Senate in midterm elections shadowed by voter opposition to the war. Decorum carried the day in the chamber – where catcalls are part of near-daily discourse – as Democrats and Republicans took their five-minute speaking turns across the hours.

Passage was a virtual certainty. Democratic leaders said they expected no more than one or two members of their rank-and-file to oppose the resolution. Republicans said that despite quiet lobbying by the White House, they expected at least two dozen GOP lawmakers to swing behind the measure, suggesting that it would receive at least 250 votes in the 435-member House.

Nick Zorn 10, a Webelos scout in Glendive, Mont., salutes as the honor guard brings Army Pvt. Matthew Zeimer's casket into Sacred Heart Catholic Church in Glendive. Zeimer was killed Feb. 2 in a firefight in Ramadi, in central Iraq. He is one of the 3,126 members of the U.S. military who have died since the beginning of the Iraq war in March 2003.

Across the Capitol, Senate Majority Leader Harry Reid said he would attempt to pass an identical measure later this month. Republicans blocked debate on a different proposal critical of the troop increase earlier this winter, after Democrats refused to give equal treatment to a GOP-backed alternative.

Democrats made clear the nonbinding measure was the beginning of a longer campaign to bring the war to an end.

“A vote of disapproval will set the stage for additional Iraq legislation, which will be coming to the House floor,” said Speaker Pelosi of California, who underscored the significance of the debate by delivering the first speech.

“In a few weeks, the war in Iraq will enter its fifth year, causing thousands of deaths, tens of thousands of casualties, costing hundreds of billions of dollars and damaging the standing of the United States in the international community. And there is no end in sight,” she said.

Boehner followed her to the well of the House seconds later, the first Republican to speak.

“There is no question that the war in Iraq has been difficult. All Americans are frustrated we haven’t seen more success more quickly,” he conceded. Pivoting quickly, he called the war in Iraq the latest in a string of conflicts dating to the founding of the nation more than two centuries ago.

“Every drop of blood that has been spilt in defense of freedom and liberty – from the American Revolution to this very moment – is for nothing if we are unwilling to stand against this threat,” he said.

Republican congressional aides said the White House was working against the measure, although presidential press secretary Tony Snow, asked if that was the case, said “no.”