Pivot to Persia On New Year's Eve 1977, President Jimmy Carter famously toasted the Shah at the Saadabad Palace in Tehran and declared, "Iran ... is an island of stability in one of the more troubled areas of the world." Less than two years later, Iran was in chaos as the revolution swept the country and brought down the 2,500-year-old monarchy. Carter has been mocked for his lack of foresight, but he wasn't wrong. He was just a few decades ahead of his time. Iraq is disintegrating. Syria is in flames. Pakistan is on the verge of becoming a failed state. The Taliban is making a comeback in Afghanistan. Libya is falling apart. The House of Saud is nervous about a potentially existential succession crisis. In this region, Iran looks like an island of stability. Meanwhile, the geopolitical enmity that has characterized relations between the United States and Iran for more than three decades has now been overtaken by events in Iraq and elsewhere. The United States seeks to reduce its footprint in the Middle East, choosing instead to focus its geopolitical energy on East Asia. And Washington's traditional allies in the Persian Gulf are funding Sunni jihadists and are anti-Shiite. In this context, the U.S.-Iran rivalry cannot be left on autopilot. News emerged on Monday that Washington and Tehran may cooperate militarily to stop the Islamic State of Iraq and al-Sham (ISIS) from advancing deeper into Iraq -- Iran's neighbor, where the United States has spent years, trillions of dollars, and thousands of lives. Iraq's Shiite government has been seen by some as a proxy of Iran that has often sided with Tehran against Washington. But the common interest between Iran and the United States is not merely tactical or temporary: With the region roiling as it is, the reality that Iran and the United States might end up on the same side is simply the new normal. While Washington may be struggling with the idea of a Persian pivot, Tehran can't seem to break from the idea that it can boost its regional position by adopting an antagonistic role against United States. Iranian officials have told me that even if the nuclear issue is resolved, U.S.-Iran relations will remain a rivalry -- not a partnership. But when radical Sunni ISIS fighters streamed across the Syrian border into Iraq and, in a matter of days, took over several major cities, the new reality became stunningly clear: Iran and the United States need each other more than ever before. Neither can salvage stability in Iraq or Afghanistan without the other. For decades, Iran has tried to challenge U.S. hegemony in the Middle East by investing in Arab political opposition groups and backing Islamist movements like Hezbollah and Hamas with funding and support. But in the Sunni Arab world, this has yielded next to nothing for Tehran. Iran's policy toward the Arab world since the 1979 revolution has been based on an accurate prediction that the reigns of the pro-American autocrats would not be durable and that Tehran's long-term security was best assured by investing in Islamist movements that likely would take over. Iran's brand of political Islam and anti-Israeli rhetoric, reasoned Tehran, could be a unifying force, bridging the deep animus that characterized the Arab-Persian and the Sunni-Shiite divides. Or so it thought. Instead, the Islamists who gained influence following the Arab Spring -- in Syria, Egypt, and Libya -- have largely shown allegiance to their financial benefactors in Saudi Arabia and the Persian Gulf sheikhdoms rather than to their supposed ideological allies in Tehran. Meanwhile, Iran's support for the Assad regime in Syria has dissipated the extensive soft power Tehran used to enjoy in the Arab world. These days, Iranian officials privately acknowledge that their government is more popular in Latin America than it is in the Middle East. The government in Tehran may find a better partner in the current administration in Washington than it might expect. Whatever America's distaste for Iran's brand of repressive Shiite nationalism, President Barack Obama knows clearly that the real threat to the United States is not the brand of Islam emanating from its nominal enemy Iran, but the one sponsored, funded, and embraced by its formal ally Saudi Arabia -- particularly if the United States and Iran manage to resolve the nuclear issue in the next few weeks or months. Obama was asked about the dangers of Sunni extremism and Shiite extremism by Bloomberg's Jeffrey Goldberg earlier this year. The Iranians, Obama said, "are strategic, and they're not impulsive. They have a worldview, and they see their interests, and they respond to costs and benefits.... They are a large, powerful country that sees itself as an important player on the world stage, and I do not think has a suicide wish, and can respond to incentives." And on Sunni extremism? Obama's silence speaks volumes. The surge of activity from radical jihadi groups likely only underlines their danger -- and the difference between them and the government of Iran. Iran is understandably hesitant about reaching out to the United States. Iran's leadership has been burned by past efforts to explore areas of strategic and tactical collaboration with the United States. Tehran provided extensive military, intelligence, and political support to the U.S. military in 2001 during the campaign to oust the Taliban. Iran's help, according to President George W. Bush's special envoy to Afghanistan Amb. Jim Dobbins, was decisive. But once Iran's help was deemed no longer necessary, Bush included Tehran in the infamous Axis of Evil speech. Washington wasn't interested in a new relationship with the Iranians. Washington has paid for that mistake ever since. Both the chaos in Afghanistan and in Iraq could have been evaded had Washington recognized the stabilizing role Iran can play if it isn't treated as an outcast. In 2003, Iran offered to help stabilize Iraq and ensure that the government there would be nonsectarian. The Bush administration chose not to respond to that offer. But Iran, too, will pay a price if it clings to an outdated understanding of the regional and global strategic landscape. Contradictory messages have come out of Tehran, with officials telling Reuters that they are open to collaboration with the United States against ISIS, and then having their Foreign Ministry spokesperson strongly oppose U.S. military intervention. Similarly, the U.S. position seems to be shifting, from first denying any plans for talking to Iran about Iraq to signaling a desire to sit down with Tehran. Iran's key objective is to be recognized as a stabilizing force. But that is a role it ultimately cannot play if it simultaneously wishes to challenge the United States. Unlike in Afghanistan, any cooperation in Iraq will likely be more public. If Iran plays a constructive role, the world will notice. But changing old patterns require courage, strength, and political will. It remains to be seen if the leadership in Tehran can deliver those -- or if Washington will be receptive. Whatever the two sides do, they should not let outdated rivalries stand in the way. If anything, the onslaught of ISIS shows that a U.S.-Iran conversation about regional matters is long overdue.