Just like love and marriage, Iran and Iraq go together. As much as the Obama administration might like to, there’s no having an “Iraq policy” without having a closely related “Iran policy.” As the song says, you can’t have one without the other.

One of the biggest failures of the administration so far is its seeming inability to coordinate its regional approach to the set of problems revolving around Iran, Iraq, and the Persian Gulf. At a conference on Monday at the American Enterprise Institute, Brian Katulis of the Center for American Progress called this “strategic incoherence.” It’s a critical failure because stability in Iraq, now at grave risk because of electoral shenanigans by Iran’s allies in Iraqi politics, is very much dependent on Iran’s role in Iraq. For years now, I’ve been writing that Iran is using its power in Iraq as leverage in regard to U.S.-Iran relations; that is, if the United States and Iran move forward toward an understanding, implicit or explicit, Iran can use its influence to stabilize Iraq, while if the U.S.-Iran dialogue spins out of control toward a showdown, Iran can turn Iraq into a seething caldron of instability and violence.

Iraqi officials, across the political spectrum, do not want Iraq to be turned into a battlefield between Iran and the United States. Yesterday, on the sidelines of a conference on the Iraqi elections organized by the Jamestown Foundation, I interviewed a senior Iraqi government official who asked that I not mention his name. “The Iranians have ties with nearly all of the main factions in Iraq,” he said, comparing Iran’s pull on Iraq to the force of gravity. “The Iranians, because of their geopolitical position in the region, will have a strong role in Iraq. So the United States, and the international community, need to reach an understanding with Iran.” Only a U.S.-Iran agreement, he suggested, can prevent Iraq from becoming a place where the U.S.-Iran tug of war is played out, and violently. Many other Iraqi officials have said the same thing, and some of them — including those who have close ties to Iran — have repeatedly offered to help mediate between Washington and Tehran. During my two visits to Iran, in 2008 and again last year, various Iranian officials have also pointed to Iraq as a place where the United States and Iran might seek an agreement.

Yesterday, at the Jamestown Conference, I asked Colin Kahl, the deputy assistant secretary of defense for the Middle East, about the importance of a U.S.-Iran accord for Iraq. But Kahl, who led Barack Obama’s campaign advisory team for the Middle East, was dismissive. “It’s debatable whether a U.S.-Iran agreement is possible,” he said. “But I don’t think it’s necessary.” Now, it’s true that a deal between Washignton and Tehran is elusive, and it will be exceedingly difficult to accomplish. But without it, Iran has so much leverage in Iraq that it can make life extremely difficult as the Obama administration draws down U.S. forces between now and 2011. Kahl discounted the importance of Iran in Iraq, saying, “I dont think there’s any probability of Iraq calling under Iranian hegemony,” and adding that those who talk about Iran’s power in Iraq underestimate the power of latent Iraqi nationalism to resist Iranian encroachment. But the point is that even though Iran may not be able to achieve hegemonic control in Iraq, it can use its muscle — from covert support to violent militias to its widely acknowledged ties to many leading Iranian Shiite religious parties — to make sure that Iraq remains unstable, violent, and prone to sectarian conflicts.

Speaking at the same conference, Zalmay Khalilzad, the former US ambassador to Iraq — who, to be sure, shares some of the blame for the Bush administration’s criminally misguided attack on Iraq in 2003 — declared that he agreed with my critique of Obama’s failure to engage in vigorous regional diplomacy with Iraq’s neighbors. “Iraq is a transition country,” he said. “It’s a transition country between Iran and the Arab world, and between Sunni and Shia. In order to make further progress in Iraq, a greater effort will be necessary at the regional level.” It will be difficult, he said, but it will be especially critical during the tumultuous period after Iraq’s March 7 election, when all of Iraq’s factions will be competing to negotiate a governing coalition.

Besides politics, Iran can meddle in Iraq using armed gangs allied to it, including the so-called League of the Righteous, aka Asaib Ahl al-Haq. Earlier this week, the Washington Post carried a feature piece on the League, an Iranian-backed militia with close ties to the perpetrators of the anti-baathist purge that has roiled the electoral scene in Iraq. Ali al-Lami, a close aide to Ahmed Chalabi, has ties to the League, and it was the Chalabi-Lami de-Baathification commission that forced the purge of hundreds of secular and nationalist candidates from the ballot. Reports the Post:

“A failed effort by the United States to neutralize a powerful Shiite militant group in Iraq has left in place a dangerous force whose attacks on American troops threaten to complicate the U.S. drawdown, according to American and Iraqi officials. …

“The U.S. military now has no more than a handful of Asaib Ahl al-Haq members in custody. American and Iraqi officials worry that violence could intensify after parliamentary elections on Sunday, particularly if Shiite candidates favored by Iran do poorly.

“‘The implicit threat is that if Iran is unable to achieve its objectives one way, it has militia groups that it can use to turn up the violence,’ said Marisa Cochrane Sullivan, a scholar at the Institute for the Study of War who has written extensively about Shiite militias. ‘The stakes are very high for Iran in this election. It’s not surprising if they’re pursuing concurring actions.'”

A year ago, President Obama launched his famous outreach to Iran, beginning with his inaugural address, in which he extended his hand to Tehran. Following that, a series of key initiatives: his taped New Year’s greeting to “the Islamic Republic of Iran,” letters from Obama to Iran’s Leader, Ayatolllah Ali Khamenei, and his well received Cairo speech on the eve of Iran’s June 12 election. Despite the post-election crisis, Obama’s diplomats held behind-the-scenes talks with Iranian officials leading up to the very important October 1 meeting in Geneva, where U.S. and Iranian diplomats met face to face for the first time in 30 years on the core issue of Washington-Tehran relations. And, at that meeting, it seemed like progress was made toward a partial resolution of the nuclear standoff, when Iran agreed to transfer the bulk of its low-enriched uranium to Russia and France for reprocessing into fuel rods for peaceful purposes.

The October 1 accord has stalled, or unraveled, and an arbitrary deadline set by Obama for the end of 2009 has come and gone, so once again the United States has turned to pressure, sanctions, and confrontation. Yet no one believes that economic sanctions will either topple Iran’s regime or cause it to halt its nuclear program, so the sanctions can only have the effect of pushing Iran into a corner. That, in turn, has many implications, but one of those implications will play out next door, in Iraq.