WASHINGTON - The new Democratic-led Congress is on a collision course with the White House over how far lawmakers can or should go to stop the war in Iraq, a dispute that could test the bounds of the Constitution. President Bush has insisted he won't back down on a decision to send 21,500 additional troops to Iraq and will ignore any resolutions passed by Congress that state opposition to his plan. The Senate is expected to consider such a measure in coming days. Some Democrats say Congress must consider tougher alternatives to force the president's hand, including cutting funding, capping the number of troops allowed in Iraq and setting an end date for the war. "This Congress was never meant to be a rubber stamp," Sen. Barbara Boxer (news, bio, voting record) told her colleagues last week. "Read the Constitution. The Congress has the power to declare war. And on multiple occasions, we used our power to end conflicts." Boxer has proposed a bill that would call for troops to come home in 180 days, allowing a minimum number to say behind to hunt down terrorists and train Iraqi security forces. But many legal scholars and congressional Republicans say such legislation is not within Congress' power. The president has control of military forces, they say. "Once Congress raises an army, it's his to command," said Robert Turner, a law professor at the University of Virginia who plans to testify Tuesday before the Senate Judiciary Committee. But whether a president needs congressional approval to wage war is up for debate among many scholars. In recent decades, presidents have routinely bypassed Congress when deploying troops to fight. Not since World War II has Congress issued an official declaration of war, despite lengthy wars fought in Vietnam and Korea. "People think Congress has to say OK to everything," said John Yoo, a former Justice Department official who helped Bush write the 2002 resolution authorizing the Iraq invasion. But if that were true "that means every war we've fought since World War II is illegal." Yoo, now a law professor at the University of California in Berkeley, said Bush's request that Congress pass a resolution authorizing force in Iraq was purely a political one. The resolution passed by a 296-133 vote in the GOP-run House and 77-23 in the Democratic-led Senate, but was not considered a declaration of war. According to Yoo, the resolution was seen solely as a way of bringing Democrats onboard. Sen. John Warner (news, bio, voting record), the former chairman of the Armed Services Committee and former Navy secretary, said he agrees Congress has no right to manage a war. "In an ongoing operation, you've got to defer to the commander in chief," said Warner, R-Va. But the veteran senator said he understands the debate that surrounds constitutional war powers and lawmakers' ability to check the executive branch. "There's always going to be this gray area between the powers of Congress and the powers of the executive branch," Warner said. "Never has been resolved, never will. We all want to leave it in a gray area." Sen. Russ Feingold (news, bio, voting record), who will chair Tuesday's hearing on war powers, says Congress shouldn't flounder on the issue when it has the ability to end the war by cutting funding for it. In coming months, the Bush administration is expected to request Congress approve at least $700 billion in military funding, giving lawmakers the clearest opportunity to pull the plug on the war. The bill is expected to include 2007 and 2008 supplemental war spending, as well as 2008 annual military spending. Rep. John Murtha (news, bio, voting record), D-Pa., who chairs the House panel that oversees defense spending, says he wants to place such stringent conditions on the funding that Bush will have no choice but to scale back U.S. involvement in Iraq. Feingold, D-Wis., proposes eliminating the war budget after six months, an approach he says will give Bush time to bring troops home without adversely affecting their well being. "Americans are not looking to Congress to pass symbolic measures, they are looking to us to stop the president's failed Iraq policy," Feingold said. "That is why we must finally break this taboo that somehow Congress can't talk about using its power of the purse to end the war in Iraq."