It is one thing to say U.S. troops must remain in Iraq until a stable government is established that does not threaten us or its neighbors. It is another thing to say -- given everything we know now -- that we ought to retrospectively conclude invading Iraq was the right thing to do.

President Bush said both things in a recent speech marking the fifth anniversary of the invasion.

"The answers are clear to me," he said. "Removing Saddam Hussein from power was the right decision -- and this is a fight America must and can win."

For President Bush to argue today that removing Saddam was the right decision is understandable. Although Congress authorized the war, Bush decided to invade. Our troops are still there -- under his command. The war is not yet won.

But do we want future presidents to decide that repeating a war like Iraq -- given everything we know now -- would be the right thing to do? Is President Bush, by defending even now his original decision to invade Iraq, authoring a new and viable doctrine of when the United States ought to go to war that Americans should endorse and embrace?

I say: No.

What if our top military and intelligence officers had in fact gone to President Bush in early 2003, before he ordered the invasion, and said: Mr. President, our initial intelligence estimates were wrong. Saddam has destroyed his weapons of mass destruction. He is not cooperating with al-Qaida. If we invade Iraq and attempt to establish a democratic government, our analysis indicates the most influential person there will be an Iranian-born fundamentalist Shiite ayatollah, who will be able to veto our political prescriptions with his fatwas.

We estimate, Mr. President, that the vacuum created by the destruction of Saddam's army will be filled by Iranian-backed Shiite militias and terrorists, indigenous Sunni insurgents and terrorists, and a newly minted Iraqi branch of al-Qaida.

No matter what kind of constitution we urge them to write, Mr. President, any elected government in Baghdad is likely to be dominated by Shiite fundamentalist parties with historical and ongoing ties to the revolutionary regime in Tehran.

And, Mr. President, we estimate we will lose about 800 U.S. troops per year in a protracted struggle with the insurgents and terrorists. Continued...