This is not to say that Congress has no constitutional leverage — only that it should exercise it responsibly. In a sense, both Bush and the more ardent opponents of the war are right. If a majority in Congress truly believes that the war is not in the national interest, then lawmakers should have the courage of their convictions and vote to stop funding U.S. involvement. They could cut the final checks in six months or so to give Bush time to manage the withdrawal. Or lawmakers could, as some Senate Democrats are proposing, revoke the authority that Congress gave Bush in 2002 to use force against Iraq.

But if Congress accepts Bush's argument that there is still hope, however faint, that the U.S. military can be effective in quelling the sectarian violence, that U.S. economic aid can yet bring about an improvement in Iraqi lives that won't be bombed away and that American diplomatic power can be harnessed to pressure Shiites and Sunnis to make peace — if Congress accepts this, then lawmakers have a duty to let the president try this "surge and leverage" strategy.

By interfering with the discretion of the commander in chief and military leaders in order to fulfill domestic political needs, Congress undermines whatever prospects remain of a successful outcome. It's absurd for House Speaker Nancy Pelosi (D-San Francisco) to try to micromanage the conflict, and the evolution of Iraqi society, with arbitrary timetables and benchmarks.

Congress should not hinder Bush's ability to seek the best possible endgame to this very bad war. The president needs the leeway to threaten, or negotiate with, Sunnis and Shiites and Kurds, Syrians and Iranians and Turks. Congress can find many ways to express its view that U.S. involvement, certainly at this level, must not go on indefinitely, but it must not limit the president's ability to maneuver at this critical juncture.