One by one, Senate Republicans are concluding the president’s surge in Iraq cannot make the kind of progress necessary to justify continued American combat there, and they are looking for new ways of backing away from Iraq without leaving chaos or a new home for terrorists. Their seriousness – and the Democrats’ – will be measured in how quickly they can find a 60-vote agreement on a redeployment plan.

The Senate has a half-dozen proposals to redefine the U.S. mission in Iraq, and while they differ in important respects, they all reduce the presence of U.S. troops, especially in Baghdad, and several emphasize the importance of expanding political and economic support to reduce violence. The differences among these plans are not important enough to prevent the Senate from agreeing on a binding redeployment of troops and a substantial expansion of diplomatic efforts as detailed in the Iraq Study Group report.

Last week, Sen. Olympia Snowe and fellow Republicans Chuck Hagel of Nebraska and Gordon Smith of Oregon joined a bill by Democratic Sens. Carl Levin of Michigan and Jack Reed of Rhode Island to begin reducing forces in Iraq in four months, with only a limited number of troops left for security and training by April 30, 2008.

Earlier this week, Sen. Susan Collins joined Democrat Ben Nelson of Nebraska to call for the start of a transition to a noncombat role for U.S. troops, who would provide protection to U.S. personnel, train Iraqi security forces, try to secure the border and continue counter-terrorism operations against al-Qaida, completing the transition by March 31, 2008.

Both bills reflect the legislation with the broadest support, a measure by Sens. Ken Salazar, a Democrat from Colorado, and Lamar Alexander, a Republican from Tennessee, and would implement the recommendations of the Iraq Study Group. Republicans John Warner of Virginia and Richard Lugar of Indiana have sponsored yet another, milder version of the study group’s recommendations.

Democratic leaders were pushing the Levin-Reed proposal, planning to meet throughout last night to highlight the issue, with votes scheduled for today. But they would stand a better chance with the Iraq Study Group plan in the Salazar-Alexander amendment, which has more support. What they cannot do is waste time making political points. With a monthlong August vacation only two weeks off, to be followed by updates on Iraq from military leaders in September, Congress either passes something before the end of July or may find itself waiting another two months before it has an opportunity to act again.

The last three months in Iraq have been the bloodiest since 2003; the goals set under the president’s surge plan may take not months but years; by January, Congress will be in full election mode and unable to agree on much of anything. Under these circumstances, the Senate has a great need to act but little time to do it. A successful vote today could make a lasting difference.