Republican senators weighing a 2008 presidential bid united behind President Bush's Iraq policy, while potential Democratic candidates favored troop withdrawals but split over a deadline for ending the U.S. military's combat presence.

"We cannot pull out and hope for the best," said Sen. John McCain, R-Ariz., calling redeployments now "a significant step on the road to disaster."

Sen. Sam Brownback, R-Kan., likewise dismissed a timetable: "We have to see this through to a successful conclusion."

However, Sen. Christopher Dodd, D-Conn., said: "We must no longer remain in an open-ended commitment."

Sen. John Kerry of Massachusetts, the Democratic nominee in the 2004 White House race, took that sentiment one step further and declared: "Setting a deadline to redeploy U.S. troops from Iraq is necessary for success in Iraq."

Back-to-back war votes showed just where the 11 senators in the crowded field of presidential wannabes stand on Iraq 18 months before the first nomination contests in the race to replace the term-limited Bush.

The GOP-controlled Senate on Thursday defeated two Democratic proposals to begin redeploying most of the 127,000 American forces in the war zone.

Bush has adamantly refused to set a withdrawal timetable.

The president contends that American troops will stay in Iraq until Iraqi security forces can defend the country against a lethal insurgency that rose up after the 2003 U.S.-led invasion toppled Saddam Hussein.

There's little doubt Bush's successor will be left to decide when to bring all American forces home. Bush himself has said as much.

Asked at a March news conference if there would come a day when there would be no more U.S. forces in Iraq, Bush said: "That, of course, is an objective. And that will be decided by future presidents and future governments of Iraq."

So, it was with this backdrop that the prospective Bush replacements in the Senate cast their votes, which Sen. John Warner R-Va., described to all senators as "one of the most important that you will ever cast."

The five Republicans ¡ª McCain, Brownback, Chuck Hagel of Nebraska, Bill Frist of Tennessee and George Allen of Virginia ¡ª stood with the president and opposed Democratic calls to withdraw forces from Iraq beginning this year.

They said a premature pullout and a public pronouncement of any such plan would risk all-out civil war, tip off terrorists, threaten U.S. security and cripple the Iraqi government just as democracy was taking hold.

"We should not limit the commander in chief's options in Iraq," Hagel said.

"Leaving Iraq to the terrorists is simply not an option," declared Frist, the Senate's majority leader.

"This is not a time to get weak in the knees," Allen agreed.

Four of the six Democrats flirting with a possible bid ¡ª Dodd, Hillary Rodham Clinton of New York, Joe Biden of Delaware and Evan Bayh of Indiana ¡ª took a middle-of-the-road approach.

They voted for a nonbinding resolution that would have urged the administration to start withdrawing troops by year's end. But they opposed the other proposal that would have carried the force of law and set a firm date by which all combat forces must be out of Iraq.

"I simply do not believe it is a strategy or a solution for the president to continue declaring an open-ended and unconditional commitment, nor do I believe it is a solution or a strategy to set a date certain for withdrawal without regard to the consequences," Clinton said.

Biden summed up his strike-a-balance position this way: "The president has a plan how not to lose, but no plan how to win. And a plan to arbitrarily set a date, in my view, to leave, is not a plan."

"We need to leave Iraq, but we need to leave it in a way that makes it as stable as possible" and that is based on "facts on the ground," Bayh, the only would-be candidate who didn't give a speech during the two-day debate, said in a statement.

The other two Democrats in the possible presidential mix, Kerry and Sen. Russ Feingold of Wisconsin, agreed to the resolution that said the Bush administration should start pulling troops out of Iraq. But they also led the effort to establish a hard date to end the military's combat mission.

It's a position embraced by the left wing of the Democratic Party, a crucial voting bloc in the presidential primary.

Under the Kerry-Feingold proposal, the administration would have been required to start withdrawing troops this year and have all combat forces out of Iraq by July 2007. The proposal would have left some troops in Iraq after that deadline to support and train Iraqi security forces, conduct counterterrorism operations and protect U.S. facilities and personnel there.

"It is time to tell the Iraqis that we have done what we can do militarily," Feingold said.

The Senate overwhelmingly defeated that plan 86-13.

Presidential ambitions ¡ª and positions on Iraq ¡ª were not lost on Senate Democratic leaders, who had written the resolution that fell on a 60-39 vote.

"I think every person who's thinking about running for president that's in the United States Senate, every Democrat, voted for our resolution," Sen. Carl Levin, D-Mich., told reporters.

"And that's a lot of people," Democratic leader Harry Reid of Nevada quipped.