Responding to the call of Pope Urban II at Claremont in 1095, the Christian knights of the First Crusade set out for the Holy Land. In 1099, Jerusalem was captured. As their port in Palestine, the Crusaders settled on Acre on the Mediterranean.

There they built the great castle that was overrun by Saladin in 1187, but retaken by Richard the Lion-Hearted in 1191. Acre became the capital of the Kingdom of Jerusalem and the stronghold of the Crusader state, which fell to the Mameluks in a bloody siege in 1291. The Christians left behind were massacred.

The ruins of Acre are now a tourist attraction.

Any who have visited this last outpost of Christendom in the Holy Land before Gen. Allenby marched into Jerusalem in 1917 cannot  on reading of the massive U.S. embassy rising in Baghdad  but think of Acre.

At a cost of $600 million, with walls able to withstand mortar and rocket fire, and space to accommodate 1,000 Americans, this mammoth embassy, largest on earth, will squat on the banks of the Tigris inside the Green Zone.

But, a decade hence, will the U.S. ambassador be occupying this imperial compound? Or will it be like the ruins of Acre?

What raises the question is a sense the United States, this time, is truly about to write off Iraq as a lost cause.

The Republican lines on Capitol Hill are crumbling. Starting with Richard Lugar, one GOP senator after another has risen to urge a drawdown of U.S. forces and a diplomatic solution to the war.

But this is non-credible. How can U.S. diplomats win at a conference table what 150,000 U.S. troops cannot secure on a battlefield?

Though Henry Kissinger was an advocate of this unnecessary war, he is not necessarily wrong when he warns of “geopolitical calamity.” Nor is Ryan Crocker, U.S. envoy in Iraq, necessarily wrong when he says a U.S. withdrawal may be the end of the American war, but it will be the start of bloodier wars in Iraq and across the region.

Iraqi Foreign Minister Hoshyar Zebari also warns of the perils of a rapid withdrawal: “The dangers vary from civil war to dividing the country to regional wars … the danger is huge. Until the Iraqi forces and institutions complete their readiness, there is a responsibility on the U.S. and other countries to stand by the Iraqi government and the Iraqi people to help build up their capabilities.”

In urging a redeployment of U.S. forces out of Iraq, and a new focus on diplomacy, Lugar listed four strategic goals. Prevent creation of a safe haven for terrorists. Prevent sectarian war from spilling out into the broader Middle East. Prevent Iran’s domination of the region. Limit the loss of U.S. credibility through the region and world as a result of a failed mission in Iraq.

But how does shrinking the U.S. military power and presence in Iraq advance any of these goals?

Longtime critics of the war like Gen. William Odom say it is already lost, and fighting on will only further bleed the country and make the ultimate price even higher. The general may be right in saying it is time to cut our losses. But we should take a hard look at what those losses may be.

It is a near certainty the U.S.-backed government will fall and those we leave behind will suffer the fate of our Vietnamese and Cambodian friends in 1975. As U.S. combat brigades move out, contractors, aid workers and diplomats left behind will be more vulnerable to assassination and kidnapping. There could be a stampede for the exit and a Saigon ending in the Green Zone.

The civil and sectarian war will surely escalate when we go, with Iran aiding its Shi’ite allies and Sunni nations aiding the Sunnis. A breakup of the country seems certain. Al-Qaeda will claim it has run the U.S. superpower out of Iraq and take the lessons it has learned to Jordan, Saudi Arabia and the Gulf states. The Turks, with an army already on the border, will go in to secure their interests in not having the Kurdish PKK operating from Iraq and in guaranteeing there is no independent Kurdistan. What will America do then?

As for this country, the argument over who is responsible for the worst strategic debacle in American history will be poisonous.

With a U.S. defeat in Iraq, U.S. prestige would plummet across the region. Who will rely on a U.S. commitment for its security? Like the British and French before us, we will be heading home from the Middle East.

What we are about to witness is how empires end.