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As the Obama administration considers cooperation with Iran in Iraq, it needs a clear understanding of Iran's intentions. Iran and Iraq are historic rivals. Tehran will only help Iraq if it serves Iran's core national interests.

Preventing Sunni terrorists from occupying the country is Iran's top priority. When Mosul was overrun by the Islamic State in Iraq and Syria (ISIS), General Qassim Suleimani, head of the Quds Force, rushed to Baghdad to advise the Iraqi Government. The day after he arrived, Ayatollah Ali al-Sistani, the leading Shiite cleric in Iraq, issued a fatwa calling on Shiites to defend the country. Thousands of volunteers headed to the front line, including battle-hardened fighters who fought in Iraq's sectarian civil war.

Shiite militias will defend shrines in Samarra, Karbala and Najaf. Iran would never let them fall to ISIS. Karbala is the site of a great battle where Hussein, Mohammed's grandson, was betrayed and slain by Sunnis. The cousin of the Prophet Mohammed is buried at the Imam Ali Shrine in Najaf. The Al-Askari Golden Dome Mosque in Samarra is the resting place of two prominent Shia imams. Protecting these shrines is a sacred duty for Shiites. Iraq's sectarian civil war started in 2006 when Sunni militants destroyed part of the golden dome.

Qassim Suleimani was the point man expanding Tehran's influence over Iraq's internal affairs and mobilizing attacks against U.S. forces between 2006 and 2008. Suleimani arranged the delivery of rocket-assisted mortars and high penetration improvised explosive devices that targeted U.S. troops. Suleimani boasted, "I don't always kill people. When I do, it's American soldiers in Iraq."

Suleimani is obsessed with America's influence in the region. Hard liners were incensed when President George W. Bush included Iran in his "axis of evil." They suspected the Bush administration of pursuing a strategy of encirclement by basing U.S. forces on Iran's borders in Iraq, Afghanistan, Pakistan, Kyrgyzstan, and Georgia.

To prevent a permanent U.S. presence in Iraq, Tehran worked behind the scenes to scuttle negotiations over the 2011 Status of Forces Agreement that would have allowed a residual U.S. force to train the Iraqi Army and assist with counter-terrorism operations.

Iraq is a geopolitical battleground for Iran, which vies for influence with Saudi Arabia in Syria and Iraq. While wealthy emirates sponsor armed Sunni terrorists, Iran supports Syria's President Bashar al-Assad in Damascus and Iraq's Prime Minister Nouri al-Maliki in Baghdad as a counterweight to Saudi influence.

Tehran also competes for influence with Turkey, a U.S. ally and NATO member. It is wary of Turkey's neo-Ottoman ambitions, and recent rapprochement with Iraqi Kurdistan. Turks and Iraqi Kurds have forged a strategic partnership, encompassing significant commercial and energy cooperation. Cooperation with Turkey makes Iraqi Kurds less reliant on Iran.

Iran is also concerned that an independent Iraqi Kurdistan would inspire unrest among Iranian Kurds. About 10 million Kurds live across the Iran-Iraq border in Iranian Kurdistan and Kermanshah. The Party for a Free Life in Kurdistan (PJAK), an armed group of Iranian Kurds, has been fighting to replace Iran's theocracy with a democratic and federal government. PJAK seeks autonomy and self-rule for all aggrieved minorities in Iran — Ahwazi Arabs, Azerbaijanis, Baluchis, and Kurds. Non-Persian ethnic groups are a potential fifth column, constituting 40 percent of the Iran's total population.

The Obama administration thinks Iraq's crisis can be solved by a more inclusive government. It believes Iran will work with it to convince Maliki to change his approach or step down.

However, Maliki emphatically rejects a government of "national salvation." Besides, Tehran put Maliki in power and will not remove him for another Shiite leader who might prove less willing to do its bidding.

Even if Iraqis arrived at a power-sharing arrangement, ISIS will not be deterred by a political solution. ISIS is a foreign army with no stake in Iraq other than destroying the country, redrawing colonial borders, and reversing a century of Arab humiliation by foreign powers.

Coordinating security with Iran is a pipe dream. Iranian drones are already in Iraqi air space and the Quds force is on the ground in Iraq. A joint command center with U.S., Iranian, and Iraqi officers is out of the question.

The U.S. should recognize that Iraq is broken and salvage what it can from the country's ruin. Instead of focusing on Baghdad, the U.S. should help secure the borders of Iraqi Kurdistan. Masoud Barzani, President of the Kurdistan Regional Government (KRG), would welcome a Status of Forces Agreement between the KRG and the United States. Even a small U.S. force in Iraqi Kurdistan would help defend Kurds from ISIS and show Tehran that the United States is still relevant in the region.

Commentary by David L. Phillips, director of the Program on Peace-building and Human Rights at Columbia University's Institute for the Study of Human Rights. He is a former senior adviser and foreign affairs expert to the U.S. Department of State during the administrations of Presidents Clinton, Bush and Obama. He is also author of the forthcoming book, "The Kurdish Spring: A New Map for the Middle East" (Transaction Publishers).