Ray Takeyh is a senior fellow at the Council on Foreign Relations.

An unusual fear is gripping the Arab world, namely that nuclear diplomacy may yet bring Iran and the United States into a close regional embrace. This may seem comical given the legacy of mistrust separating the two nations. Yet this concern among Arab rulers, fueled by progress toward a final agreement on Tehran’s nuclear program, may have some justification in history. The United States has never been able to pursue arms control without delusion and has always insisted on sanctifying its negotiating partners, conjuring up moderates and searching for common ground. The challenge for Washington today is to defy its history and reach a nuclear agreement with Iran while negating the Islamic Republic’s regional ambitions.

During the heydays of detente in the 1970s, nuclear accords between the United States and Soviet Union were inevitably followed by commerce and diplomatic recognition. Successive U.S. administrations were seduced by the notion that a nuclear agreement could pave the way for grander geopolitical convergence. If the thorny nuclear issues could be resolved through cool-headed dialogue, the thinking went, then why not other areas of superpower contention? This proved a fools’ errand, as the Kremlin saw no contradiction between negotiating a treaty on arms limitation and invading Afghanistan. U.S. adversaries have always been more practical about arms control and have seldom forfeited their ideological claims for the sake of trade and reconciliation.

On the surface, the chimera of bringing Iran in from the cold could prove equally alluring. After all, the resurgence of al-Qaeda, a radical Sunni movement, argues for cooperation with an alarmed Shiite state. The United States is seeking to leave its war-torn charge in Afghanistan and may yet need Tehran’s assistance for such a withdrawal. Perhaps once the two sides have agreed on the nuclear file, they could move toward a larger canvass of cooperation. These sober strategic arguments are seemingly buttressed by the rise of pragmatists led by President Hassan Rouhani. As such, a concerted U.S. effort at engagement might foster Iranian moderation in its foreign policy as well as strengthen the forces of progressive change domestically.

Like their Soviet predecessors, the guardians of Iranian theocracy are far less sentimental than Americans about their diplomacy. Whatever confidence-building measures Iranian diplomats may be negotiating in Geneva, supreme leader Ali Khamenei insisted as recently as late November that Iran is “challenging the influence of America in the region and is extending its own influence.” In Khamenei’s telling, the United States is a crestfallen imperial power unable to impose discipline on a recalcitrant Middle East. It is not his burden to salvage the wreckage of the United States but merely to fill the vacuums left by its abdication.

The key actors defining Iran’s regional policy are not its urbane diplomats mingling with their Western counterparts in Geneva but the Revolutionary Guard Corps, particularly the famed Quds Force. For the force’s commander, Qassem Suleimani, the struggle to evict the United States from the Middle East began in Iraq, as Suleimani proclaimed in September. The struggle has moved on to Syria. The survival and success of the Assad dynasty is now a central element of Iran’s foreign policy.

The U.S. task remains imposing stringent limits on Iran’s nuclear program through negotiations while restraining Tehran’s regional ambitions through pressure. This latter goal will require mending the United States’ battered alliances in the Middle East. Strategic dialogues and arms sales can go only so far. The United States cannot reclaim its allies’ confidence without being an active player in the Syria saga. To be sure, Syria’s opposition is fragmented and the rise of Islamist radicals is a troubling sign, but many are still committed to displacing Assad and taming Islamist militancy — and they are worthy of Western embrace and support. As long as the United States exempts itself from this conflict, its other pledges ring hollow to a skeptical Arab audience.

Too often tensions between the United States and Iran have been attributed to technical disagreements over the scope of Tehran’s nuclear program. For decades, diplomats have struggled to define just the right balance between centrifuges and sanctions relief. Those negotiations have taken place while Iran’s presidency has changed hands from reformers to hard-liners and now, finally, to pragmatists. At the core this conflict is ideological: Iran does not want us to succeed, and we should not want Tehran to prevail. Iran’s assault on the Arab order will define the parameters of Middle East politics for some time to come. The first step toward a sensible Iran policy is to dispense with the illusion of detente that too often accompanies arms control diplomacy.