'Everywhere you turn, it is the policy of Iran to foment instability and chaos," Defense Secretary Robert Gates warned Gulf dignitaries in Bahrain last month. But in reality, everywhere you turn, from Qatar to Saudi Arabia to Egypt, you now see Iranian leaders shattering longstanding taboos by meeting cordially with their Arab counterparts.

The Gulf has moved away from American arguments for isolating Iran. American policymakers need to do the same.

The states of the Gulf Cooperation Council (GCC) are accommodating themselves to Iran's growing weight in the region's politics. They remain key parts of America's security architecture in the region, hosting massive US military bases and underwriting the American economy in exchange for protection. But as Saudi analyst Khalid al-Dakheel argues, they are no longer content sitting passively beneath the US security umbrella and want to avoid being a pawn in the US-Iranian struggle for power. Flush with cash, they are not interested in a war that would mess up business.

That's why America's attempt to shore up containment against Iran increasingly seems to be yesterday's battle. On Dec. 3, Iranian President Mahmoud Ahmadinejad addressed the GCC in Doha, Qatar. It was the first time an Iranian leader had addressed the alliance, which was formed in 1981 against the Iranian challenge.

Weeks later, Saudi King Abdullah invited Mr. Ahmadinejad to Saudi Arabia – the president's third visit in a year – for the hajj, or Muslim pilgrimage to Mecca. The king used the occasion to hold cordial talks.

Iran is even reaching out to Egypt. Ali Larijani, head of Iran's National Security Council, visited Cairo recently for the highest level talks in 27 years. Afterward, Arab League chief Amr Moussa bluntly stated that there was no point in Arabs treating Iran as an enemy.

Gulf Arabs have thus visibly discarded the central pillar of the past year of America's Middle East strategy. Saudis and Egyptians had been the prime movers in anti-Iranian and anti-Shiite agitation. When they are inviting Ahmadinejad and Mr. Larijani to their capitals, America's talk of isolating Iran sounds outdated.

One hears little today of the "Shiite crescent" threatening the region, against which Arab officials once gravely warned. The Bush administration's proposed "axis of moderation," joining Sunni Arab states and Israel against Iran, has quietly passed from view.

Meanwhile, the GCC seems more unified and confident than it has in years. Earlier this week the six member countries agreed to form a common market. Saudi Arabia and Qatar have mended fences. Pressures for domestic political reforms have been largely defanged, and the oil bonanza has allowed Saudi Arabia to pursue an energetic foreign policy. The Gulf states won't abandon their US protectors anytime soon, but they seem more willing than ever to act on their own initiative.

The emerging signs of a tentative thaw in the Gulf are not due solely to the release of the findings in last month's National Intelligence Estimate (NIE) that Iran was no longer pursuing a nuclear weapons program. The NIE helped trigger the thaw by convincing Arabs that a US-led war against Iran had become much less likely. But it has long been clear that most Gulf rulers have no appetite for a war that would disrupt their economic boom and put them at the most risk. The Gulf media today speaks more of avoiding war than of fomenting it.

Even in Iraq, fears of a Saudi-Iranian proxy war have given way to hints of an emerging modus vivendi. Gulf regimes remain hostile to the pro-Iranian Iraqi government. But instead of trying to replace its Shiite leader, Nouri al-Maliki, they now seem satisfied that the rise of the Sunni "Awakenings" – US-backed neighborhood councils that have begun fighting Al Qaeda – will check Iranian ambitions. Saudi and Iranian clients in Iraq even seem to be carving out zones of influence, as suggested by recent talks between the Sunni Anbar Salvation Council and the Shiite Supreme Islamic Iraqi Council.

This is not to say that the Gulf states are comfortable with Iranian power. Anti-Shiite and anti-Persian sentiment exists throughout the Gulf. Iran's territorial dispute with the United Arab Emirates generates considerable passion in that country. Few Gulf or Arab leaders publicly welcome an Iranian nuclear program. And Ahmadinejad's proposal of a new Gulf security architecture including Iran was widely seen as an initiative for Iranian hegemony, not a genuine collective security arrangement.

Gulf states see Iran as a challenge that they have been dealing with for decades, not an urgent or existential threat. The shifting Arab approach may leave the US with little choice but to do the same. Just as America's containment of Iraq began to collapse in the late 1990s when its Arab neighbors lost faith in the value of sanctions, the new Gulf attitudes will probably now shape what the US can do with Iran.

• Marc Lynch is a professor of political science and international affairs at George Washington University.