The diplomatic bargain struck by the United States and Iran this week is the Obama administration's greatest diplomatic triumph. Efforts by the US Congress to derail it would, if successful, constitute a self-inflicted strategic wound even more myopic than its vote to endorse the 2003 invasion of Iraq. That vote, after all, was only endorsing a mistaken policy set in the White House. This one would be a rebellion against a White House decision that promises great benefits to the United States.

Congress, it turns out, is filled with Republicans and Democrats eager to act as enablers for the most repressive forces in Iran. It is an astonishing spectacle: an alliance between brutal Iranian institutions, principally the Revolutionary Guard, and elected representatives of the American people. Both are deeply invested in the paradigm of hostility, and both are in a state of near-panic at the prospect of reconciliation between Tehran and Washington.

Hostility toward Iran may not be the silliest of all American foreign policies –that would probably be the continuing trade embargo of Cuba – but it is undoubtedly the most self-defeating. No step the United States could take anywhere in the world would bring strategic benefits as great as détente with Iran. It has tantalizing potential. Iran's interest in stabilizing the violence-torn countries on its eastern and western borders, Iraq and Afghanistan, closely parallels that of the United States.

In recent days, much has been made of al-Qaida's takeover of the Iraqi city of Falluja, where dozens of American soldiers were killed in 2003-4 and the bodies of several memorably strung up from a bridge. It is indeed painful to reflect that the blood of those soldiers may have been wasted. But since the United States is not prepared to return to Iraq, what can it do to stop the advance of radical militants there? Iran, the neighboring power, is even more opposed to al-Qaida than is the United States, and even more eager to support the Shiite-led government in Baghdad. It is the west's logical partner in that fight.

Iran can help douse fires that threaten to engulf the Middle East and surrounding regions. But those fires, awful as they are, do not truly threaten the United States. One development in that part of the world, however, has devastated Iranian society and is killing Americans every day: heroin trafficking. Nearly all the world's heroin comes from poppies grown in Afghanistan. In recent years heroin addiction has become a full-blown national crisis in Iran, and last week Governor Peter Shumlin of Vermont asserted in a dramatic speech that his state, like others in the US, is facing a "full-blown heroin crisis". That makes the Afghan heroin trade and the metastasizing violence of al-Qaida two enemies that threaten both the US and Iran. If these two countries can begin working together, they will be more able to confront these two scourges than either could do alone.

This week's accord with Iran, which was signed by five other powers in addition to the US, is the first step in what could become a process that will prevent Iran from developing nuclear weapons and allow it to work with the west in confronting serious security threats. Beyond that, it lays the basis for a process that could turn Iran into a normal country that respects basic human rights at home and exports stability instead of instability. There is no chance that America's longstanding Arab ally, Saudi Arabia, could evolve that way. Yet this deal has evoked passionate opposition in Washington. Why?

It is a safe bet that many of members of Congress, including more than a few of the 59 senators now trying to kill the US-Iran peace process, would struggle to identify Iran on a map. Many, however, cling to the belief that the only true test of any American foreign policy is whether Israeli leaders support it. The Israel lobby in Washington has turned the Iran deal into a life-or-death struggle. It is no accident that leaders of the war party, like Senator Mark Kirk of Illinois, have received huge amounts of campaign money from that lobby. Nor is it strange that Hillary Clinton, who is eager for the lobby's support in her upcoming presidential campaign, has been deafeningly silent on this issue.

The strategic logic of rapprochement between the US and Iran is clear. If the deal now taking shape holds, it will promote American security interests and could begin a profound process of transition within Iran. The campaign against it, while perhaps logical in the eyes of politicians looking for campaign donations, is based on stupefying ignorance. Blocking this deal would be an act of diplomatic vandalism as damaging as any that Congress has inflicted in living memory.