Our last best hope in Iraq — General David Petraeus — reminded Pentagon reporters this week of a critically important fact long forgotten by most observers: Our real enemy in Iraq, the true source of all the murders, mayhem, and instability, is not sectarian strife. And it’s not the Sunnis or the Shiites either. The real enemy we face in Iraq is Al Qaeda.

According to the top American commander in Iraq, Al Qaeda’s number one priority is defeating America in Iraq. The general called this organization “public enemy number one,” adding that “Iraq is, in fact, the central front of al Qaeda’s global campaign.”

The Senate majority leader, Harry Reid, doesn’t understand this. Nor for that matter, do the other defeatist Democrats carelessly demanding our immediate withdrawal. They fail to grasp that the root of our problems in Iraq — again, the true source of the hostilities — remains Al Qaeda. These murderous thugs are fomenting the sectarian strife on both sides of the Iraqi street. Their tactic is the nadir of nihilism.

In contrast to the blind Harry Reid contingent, I’d like to highlight one remarkably clear thinker who does get what’s going on in this war — someone who recognizes the true enemy and is able to articulate his position in breathtaking clarity. I’m talking about Senator Lieberman of Connecticut. Frankly, no public official understands what’s at play better than Mr. Lieberman. He set forth his lucid position in Thursday’s Washington Post, and brought it alive when I interviewed him on “Kudlow & Company” later that day.

Mr. Lieberman forcefully stated that “Al-Qaeda, after all, isn’t carrying out mass murder against civilians in the streets of Baghdad because it wants a more equitable distribution of oil revenue. Its aim in Iraq isn’t to get a seat at the political table; it wants to blow up the table — along with everyone seated at it.” (Emphasis added).

To miss this point is to miss the crux of this conflict. There can be no doubt about the central role being played by Al Qaeda in this war. Their domination of the Iraqi theater is unmistakable. They are the hinge of this war. And, lest we forget, these are the same murderers who bombed us on September 11, 2001. They are terrorists who have made crystal clear their intention to subvert us at every turn. And make no mistake about it — they are regrouping in order to strike us again.

This is why the stakes are so high, and why we must not interrupt the surge. This is why there can never be a so-called “political settlement” unless and until America can militarily cripple Al Qaeda in Iraq. Only then can a political settlement be reached, one that can provide for a healthy, representative government, oil sharing, proportional staffing in ministries, and on down the line.

Without question, it is a near certainty that Iran and Syria are helping Al Qaeda with money, arms, and explosives. And yes, if we leave now, Al Qaeda will have an open field in which to expand their operations and prepare for the ultimate attack on America. In fact, the Defense Department and the CIA just nabbed a high-ranking Al Qaeda operative known as al Iraqi. He was a key link between the Taliban in Afghanistan, Al Qaeda in Iraq, and Al Qaeda members in Iran. And while it’s great news we got him, he’s one more reminder that this network is strong and playing for keeps.

Another reality, too often overlooked, is that America successfully removed Saddam Hussein from the world scene. We ended a ruthless, tyrannical dictatorship. We fostered three heavily participated elections in Iraq, and helped establish a new democratic government in the center of the Middle East. These are important accomplishments. Yet the stated goal of Al Qaeda is to sabotage all of this. Their aim is to prevent representative government in the region, since their twisted totalitarian ideology opposes such developed-world things.

The Harry Reids in Washington don’t get it. They fail to see the terrorist fingerprints. But when you look at Iraq through the Lieberman lens, the dust settles. The task before us becomes clearer. Why are we in Iraq? We are fighting Al Qaeda. Period.

A final question for Mr. Reid: If, as he says, we have “lost” the Iraq war, who exactly has won? Who is the winner, Senator Reid? Who would you like America to surrender to?

It’s not the Sunnis. It’s not the Baathists. It’s not the Shiites. And it’s certainly not Prime Minister Maliki. In conventional warfare terms, Harry Reid is suggesting we surrender to Al Qaeda.

Does the majority leader of the Senate understand his own unthinkable conclusion?

Mr. Kudlow is host of CNBC’s “Kudlow & Company.”