And now for a reality check on the congressional debate about leaving Iraq.

Neither Democrats nor Republicans have a grip.

Republicans are right to nix the idea that U.S. troops should withdraw in six months. But the Bush administration has made such a hash in Iraq that U.S. troops have little chance of creating the "secure and united Iraq" that Republicans call for.

Bad U.S. policy and worse execution have left Americans with two unpleasant choices: leave Iraq now and ensure that country's collapse, with awful consequences for them, us and the entire Middle East; or stay on with no guarantee that perseverance will stabilize the country.

No wonder Democrats are frustrated; in such circumstances, it's hard for the most cogent critic to fashion a better policy.

The Democrats know the Bush administration created a new beachhead for Islamist terrorists in Iraq that didn't exist before. They know the administration refrained from taking out Abu Musab al-Zarqawi in 2003, when he was a small fry in Iraqi Kurdistan; Kurdish intelligence officers urged U.S. officials in vain to bomb him. They know all this — even as Karl Rove claims that if Democrats had had their way, Zarqawi would never have been killed.

No wonder many Democrats rage at administration hypocrisy. However, a policy based on anger won't work.

To understand the hard choices ahead, think of the U.S. troop presence as fingers in a crumbling dike surrounding Iraq. Pull them out now, and the dike will collapse; a New Orleans-level flood will inundate the region and send huge waves in our direction.

Keep the fingers in, and the dike will eventually collapse anyway unless it is shored up in the meantime. Everything depends on whether the new Iraqi government (and a more realistic White House) can pile on enough concrete slabs before the dike gives way.

In my latest trip to Iraq earlier this month, elected Iraqi political leaders from all communities — Shiite, Kurd and Sunni — told me U.S. troops should not be withdrawn now. Having dismantled all the institutions that held Iraq together, the United States has a moral obligation to help the new Iraqi government rebuild, according to these leaders — especially since U.S. officials have failed so badly, so far, in reconstruction efforts.

Iraqi leaders also say the violence would not die down if Americans leave now. Instead, it would grow much, much worse.

Some Sunni insurgents who are fighting purely against U.S. occupation might return home. But the insurgent core of Baathists and Islamists are engaged in a struggle for power against the new majority of Shiites and Kurds. They are also out to destroy moderate Sunnis who are willing to join the new Iraqi system. That fight would go on.

Indeed, if U.S. troops leave too soon, Iraq could become a regional battlefield, with Iran supporting Iraqi Shiites, and Sunni Arab states giving aid to Iraqi Sunni fighters. Such a battle could rage indecisively for years as Sunni areas became a haven for terrorist training, creating an Islamist threat to the entire region.

But will the situation get better if the Americans maintain a large presence for a couple of years?

This depends on whether the new Iraqi government can perform. No one knows if its Shiite and Sunni leaders can reconcile and, together, undercut the core insurgents. U.S. officials would have to mediate. They would have to pony up more economic aid for Iraq from U.S. allies, including Arab countries (our aid funds, badly used, are running out). The White House would also have to promote a regional accord that pressed Iraq's neighbors to stop meddling in Iraqi affairs. All a very tall order.

But the costs of failure are so high that this new government must be given a chance over the next year. U.S. troops will be drawing down in 2007, because our military is overextended. By 2007, Iraqi officials will be asking for a status-of-forces agreement that defines where and how remaining troops will be used. Prime Minister Nouri al-Maliki says Iraq should take control of its security in 18 months.

In the meantime, Democrats should swallow their anger (and stop booing Sen. Hillary Rodham Clinton for opposing a timetable). Republicans should swallow their hubris; there are no guarantees that "staying the course" will produce the "victory" of their dreams. Everything depends on whether the Iraqi dike can be shored up before the floodwaters overwhelm Baghdad — and then head toward us.

Trudy Rubin is a columnist and editorialboard member for the Philadelphia Inquirer. Reach her at www.trubinphillynews.com.