While Democrats and Republicans squabble in Congress, they deserve bipartisan credit for one stunning achievement: the defeat of the United States in Iraq.

The willful blindness and strategic stupidity of the Bush administration led us into the Iraq War and the postwar disaster. The 2007 troop surge and Gen. David Petraeus created a slim hope that Iraq might yet become stable. That hope was dashed by the mistakes of the Obama team.

As U.S. troops finish their pullout by year’s end, no fine farewells can disguise the sad realities on the ground. Iraq today is a broken country where sectarian strife is re-emerging and al-Qaida is seeking a comeback. Prime Minister Nouri al-Maliki acts like an autocrat and marginalizes Iraqi moderates. He also depends for his political survival on Tehran’s blessing.

Indeed, the paramount victors to emerge from our Iraq misadventure are the ayatollahs of Iran.

The lion’s share of blame for this debacle rests with the Bush team, which ignored the likely consequences of the war. Wishful thinking became a substitute for strategy; real Mideast expertise was rebuffed. (This tendency is all too alive in the current, careless rhetoric about attacking Iran emanating from several Republican presidential hopefuls.)

Bush officials believed ousting Saddam Hussein would lead to pro-American regimes from Baghdad to Tehran. I will never forget Deputy Secretary of Defense Paul Wolfowitz telling me in November 2002 that postwar Iraq would resemble post-World War II France, where we liberated the country and left.

Instead, White House ignorance about Iraq — and the decision to disband its army — produced a security collapse in the country, a bloody sectarian war, and the emergence of al-Qaida in Iraq.

When Bush officials finally started acting as occupiers, they set up a governing system that encouraged representation by religious and ethnic parties. This system ensured that Shiite religious groups would dominate Iraq’s political system and played right into the hands of Iran.

Fast-forward to Barack Obama’s election in 2008. Petraeus had defanged Sunni insurgents and new Prime Minister Maliki had cracked down on murderous, pro-Iranian Shiite militias. There was a chance, albeit slim, that a new nationalist Iraqi politics could emerge that would keep Iran at bay. Serious and smart U.S. diplomacy was essential to make that happen.

Instead, the Obama team focused mainly on quitting Iraq by the end of 2011 — a pledge made by Obama (and also by Bush). The White House followed a hands-off policy on Iraqi politics, allowing Maliki to slip back into sectarianism and the eager embrace of Iran’s ayatollahs.

When Maliki cracked down on Sunni candidates before the March 2010 elections, a visiting Vice President Biden gave him a pass. When a Sunni coalition called Iraqiya edged out Maliki’s party and he used Iraq’s politicized courts to nullify some Sunni seats, U.S. officials didn’t push back.

When Maliki sent security forces in February to crush Iraq’s Arab Spring demonstrators, who were protesting his regime’s corruption, the administration didn’t protest. The Obama team constantly repeats that Iraq is a “sovereign nation,” but of course sovereignty made little difference when we backed demonstrators in Libya, Tunisia and Egypt.

When Maliki failed to honor a power-sharing deal the United States had brokered between his party and Iraqiya, we failed to press him. That deal would have produced a secular-nationalist-oriented government in Baghdad, something Biden should have fought for. Inexplicably, he didn’t.

Maliki opted instead for a sectarian Shiite alliance brokered in Tehran, which is dependent on the radical, Shiite faction of Muqtada al-Sadr. Although Maliki dislikes Iran, as he hinted during his visit to the White House last week, he made himself dependent on the ayatollahs in order to keep his hold on power.

The U.S. failure to back the power-sharing deal it brokered had other negative repercussions. It helped doom U.S.-Iraqi negotiations for a small U.S. military presence after 2011. That presence would have sent a critical message to Iran that Iraq wasn’t a plum for the taking.

Biden, who had the Iraq file, didn’t visit the country in the crucial months of this year when the agreement was being negotiated. “If the administration had worked hard to implement the power-sharing deal they might have gotten an agreement [on the troop presence],” says Ned Parker, an experienced Iraq hand and journalist who is the Edward R. Murrow fellow at the Council on Foreign Relations.

Instead, many secular Iraqis concluded we weren’t willing to stand up to Tehran, so why should they risk death threats from the Sadrists? The result: We’ll soon be gone and Iran will rush to fill the vacuum we’ve left.

Already, the Sadrists are threatening the thousands of U.S. diplomats who will stay on. This serious security risk makes it unlikely that our diplomats will be able to get out of the huge embassy complex and travel the country to implement joint civilian programs. In U.S. military circles, they are talking about the embassy becoming “a five-star prison.”

Bush’s aggressiveness broke Iraq. But Obama’s passivity consigned Iraq to Tehran’s orbit. Together, Republicans and Democrats have produced an Iraq that has inspired not the Arab Spring but sectarian warfare and anti-American hatred. And both parties have betrayed Iraqis who believed in democracy and American promises.

This is a bipartisan achievement of which no one should be proud.