After nearly four years of confusing arguments over the invasion of Iraq, the debate has suddenly and unexpectedly taken on a sort of weird simplicity. The Democrats, after dividing on whether to support the attack when it began, and then adopting (individually) almost every conceivable position regarding it since, have now, together with Republican senator Chuck Hagel of Nebraska, more or less united on a single demand: bring our troops home, and let the Middle East settle its own problems.

And President Bush, after years of insisting we were on the path to "victory" and had only to "stay the course," has decided to send an additional 21,500 troops to Iraq in one last attempt to impose our will on events there. As commander in chief, that decision was his to make, and surely most Americans will hope that this "surge" succeeds. But if it fails, there is equally little doubt that our military operations in Iraq will soon be winding down, and George W. Bush's legacy in foreign affairs will be one of abject failure.

In pure theory, Bush's opponents could afford to wish him good luck in the "surge," and simply sit back and wait to see what happens. If he is successful, the egg will be on their faces. If he isn't, they will be reaping the political rewards for years to come.

But the Democrats, perhaps inevitably, have been unable to resist the temptation to go on record as supporting what polls indicate is the conclusion of about three-quarters of the American people: that the war in Iraq isn't winnable, at least at any price in blood and treasure that they are willing to pay. So the congressional hoppers are full of "non-binding resolutions" demanding that Bush quit now, without a "surge" or any other effort to achieve a better outcome. All of these will be filibustered to death, if necessary, by the Senate Republicans, far more than the necessary 40 of whom are sticking by the president and are in no mood to let the Democrats indulge in such grandstanding. Even so, however, such gestures serve to register the Democrats' solid agreement with most voters, and that never hurts.

Meanwhile, outside of Congress, the militant left, which privately despises the United States and longs for its defeat, is busy staging mass rallies in furtherance of that cause.

It is too early to predict the course of events in Iraq. Certainly the record of the past four years isn't encouraging. But Bush's admission, in his State of the Union address, that the strategy of restraint -- of minimizing the American presence and pushing the Iraqis, prematurely, to assume the leading role -- simply hasn't worked, and must be drastically revised, will, in and of itself, generate a different dynamic, and therefore, just possibly, a different result.

Meanwhile the so-called "insurgents," not to mention their abettors in Iran and Syria, are watching the debate in the United States with what must surely be considerable satisfaction. They have never imagined they could defeat this country in a conventional war. But they learned from Vietnam, along with the rest of the world, that the American people have no stomach for long military operations against guerillas who can avoid extinction and impose fatalities -- few, perhaps, but persistent and seemingly endless -- on American troops. Sooner or later, they are gambling, our will and patience will give out, and our healthy democratic processes will force the government to abandon Iraq and probably the rest of the Middle East.

Whether they would be satisfied with that achievement, or simply conclude that it points the way to the ultimate Islamic conquest of the West, remains to be seen.