WASHINGTON (CNN) -- The Senate on Thursday approved a $124 billion war spending bill that calls for U.S. combat troops to leave Iraq in 2008, sending the measure to the White House for a threatened veto by President Bush.

The bill's 51-46 margin is far short of the two-thirds vote needed to override a presidential veto, which Bush says he will deliver swiftly. The House passed the same measure on a 218-208 vote Wednesday night.

Senate Majority Leader Harry Reid, D-Nev., said the measure funds U.S. troops in the field while acknowledging that the 4-year-old war needs a political, not military, solution.

"No one wants this nation to succeed in the Middle East more than I do," Reid said. "But I know that after four years of mismanagement and incompetence by this administration in the war in Iraq, there is no magic formula, no silver bullet that will lead us to the victory we all desire."

But Republicans said the bill amounted to an admission of defeat.

"We must give the plan for winning the military component of the war in Iraq a real chance to succeed," said Sen. Mitch McConnell, R-Ky. "Without it there is no political solution."

Two Republicans -- Sens. Chuck Hagel of Nebraska and Gordon Smith of Oregon -- joined Democrats to support the bill. Connecticut independent Joseph Lieberman, who caucuses with the Democrats, joined Republicans in opposing it.