By Thomas L. Friedman

President Bush's Iraq surge policy is about a month old now, and there is only one thing you can say about it for certain: no matter what anyone in Congress, the military or the public has to say, it's going ahead. The president has the authority to do it and the veto power to prevent anyone from stopping him. Therefore, there's only one position to have on the surge anymore: hope that it works.

Does this mean that Democrats in Congress who are trying to shut down the war and force a deadline should take the advice of critics and shut up and let the surge play out?

No, just the opposite. I would argue that for the first time we have -- by accident -- the sort of balanced policy trio that had we had it in place four years go might have spared us the mess of today. It's the Pelosi-Petraeus-Bush troika.

I hope the Democrats, under Speaker Nancy Pelosi, keep pushing to set a deadline for withdrawal from Iraq, because they are providing two patriotic services that the Republicans failed to offer in the previous four years: The first is policy discipline. Had Republicans spent the previous four years regularly questioning Don Rumsfeld's ignorant bromides and demanding that the White House account for failures in Iraq, we might have had the surge in 2003 -- when it was obvious we did not have enough troops on the ground -- rather than in 2007, when the chances of success are much diminished.

Because the Republicans controlled the House and Senate, and because many conservatives sat in mute silence the last four years, the administration could too easily ignore its critics and drag out policies in Iraq that were not working. With the Democrats back in Congressional control, that is no longer possible.

The other useful function Speaker Pelosi and her colleagues are performing is to give the president and Gen. David Petraeus, our commander in Iraq, the leverage of a deadline without a formal deadline. How so? The surge can't work without political reconciliation among Iraqi factions, which means Sunni-Shiite negotiations -- and such negotiations are unlikely to work without America having the ''leverage'' of telling the parties that if they don't compromise, we will leave. (Deadlines matter. At some point, Iraqis have to figure this out themselves.)

Since Mr. Bush refuses to set a deadline, Speaker Pelosi is the next best thing. Do not underestimate how useful it is for General Petraeus to be able to say to Iraqi politicians: ''Look guys, Pelosi's mad as hell -- and she has a big following! I don't want to quit, but Americans won't stick with this forever. I only have a few months.''

Speaker Pelosi: Keep the heat on.

As for General Petraeus, I have no idea whether his military strategy is right, but at least he has one -- and he has stated that by ''late summer'' we should know if it's working. As General Petraeus told the BBC last week, ''I have an obligation to the young men and women in uniform out here, that if I think it's not going to happen, to tell them that it's not going to happen, and there needs to be a change.''

We need to root for General Petraeus to succeed, and hold him to those words if he doesn't -- not only for the sake of the soldiers on the ground, but also so that Mr. Bush is not allowed to drag the war out until the end of his term, and then leave it for his successor to unwind.

But how will General Petraeus or Congress judge if the surge is working? It may be obvious, but it may not be. It will likely require looking beneath the surface calm of any Iraqi neighborhood -- where violence has been smothered by the surge of U.S. troops -- and trying to figure out: what will happen here when those U.S. troops leave? Remember, enough U.S. troops can quiet any neighborhood for a while. The real test is whether a self-sustaining Iraqi army and political consensus are being put in place that can hold after we leave.

It will also likely require asking: Are the Shiite neighborhoods quieting down as a result of reconciliation or because their forces are just lying low so the U.S. will focus on whacking the Sunnis -- in effect, carrying out the civil war on the Shiites' behalf, so that when we leave they can dominate more easily?

When you're sitting on a volcano, it is never easy to tell exactly what is happening underneath -- or what will happen if you move. But those are the judgments we may soon have to make. In the meantime, since Bush is going to be Bush, let Pelosi be Pelosi and Petraeus be Petraeus -- and hope for the best. For now, we don't have much choice.