The attacks come as the U.S. military presence in Iraq has fallen to below the symbolic number of 50,000 troopers and seem to serve as a confirmation of the widely held belief that the presence of U.S. forces in Iraq has been but a finger in a badly broken dam.

"From the day of the fall of Saddam until now, this is what we have - explosions, killing and looting," Khalil Ahmed, a 30-year-old engineer, told The New York Times. "This is our destiny. It's already written for us."

It's not particularly fruitful to wonder "what if?" But surely, if the security gains of the past two years crumble in the wake of the American withdrawal, many who now believe the Bush-ordered "surge" was a success may begin to wonder whether it was all for naught. If this is, as Mr. Ahmed suggested, Iraq's destiny, then what did it matter if U.S. soldiers stood up - and sometimes fell - in an effort to make room for the fledgling Iraqi government to grow into its very big britches. What did those thousands of American lives buy for Iraq? For the United States?

And if Iraq crumbles there will, of course, be those who say that President Obama acted too hastily in drawing down combat forces. Clearly, he had little political choice. The president came to power largely on his opposition to the war in Iraq - and his promise to bring home U.S. troops from one of the worst foreign quagmires in American history. Nearly two-thirds of Americans say they oppose that war and a slightly greater number say they approve of Obama's plan to drawdown forces and end combat operations in Iraq.

But what of the moral choice? When you are the boy with his finger in the dam. If hundreds, thousands, millions of lives depended upon you staying right where you are, keeping your finger in a hole that you created, in a dam that history constructed...

... what would you do?

Alas, it's all a thought exercise. A game of theoretics.

What is done is done. And now, the dam will stand - or fall - on its own.