If there’s one thing the huge (and growing) field of Democratic presidential aspirants largely agrees on, it’s that the U.S. ought to re-enter the 2015 nuclear deal with Iran. This week, Pete Buttigieg and Beto O’Rourke became the latest to join the chorus. Unfortunately, going down this path would be a big mistake – and a missed opportunity.

Known as the Joint Comprehensive Plan of Action, the nuclear deal was negotiated by President Barack Obama’s administration and agreed to by Iran and six world powers in 2015. In essence, it sought to impose a 25-year quarantine on the Islamic Republic’s ability to develop nuclear weapons. Last year, President Trump unilaterally terminated the agreement.

Although Trump’s decision was rash, it wasn’t wrong. The deal was fatally flawed. Even as it was being negotiated, critics in the Middle East and beyond complained that the Obama administration was ignoring Iran’s destabilizing activities in the region. They feared the regime would use the political cover provided by the Joint Comprehensive Plan of Action to step up its threatening behavior.

They were right. Since the deal, Iran has only grown more belligerent. In Syria, it has helped President Bashar Assad slaughter his own citizens. In Lebanon and Palestine, Iraq and Yemen, it has continued to arm brutal proxy fighters. It has only intensified its pursuit of ballistic-missile technology and its cyberattacks against the U.S. If an agreement limited to nuclear weapons was too narrow in 2015, Iran’s actions since have made such a deal entirely insufficient.

With Trump’s policies doing little to curtail this behavior, Democratic candidates should seize the opportunity to push for a new deal. Rather than merely bringing the U.S. back into the Joint Comprehensive Plan of Action, they should insist on a broader, genuinely comprehensive bargain that fixes the defects in the original and takes into account Iran’s recent aggression.

A new deal should require Iran to forswear not only nuclear weapons, but also missiles capable of carrying them. It should demand that the regime cease its other threatening activities in the region and allow for more intrusive and aggressive monitoring than that stipulated in the original agreement. It should also spell out tough sanctions that Iran would incur if it strays from the terms.

Iran’s incentives to reopen talks, meanwhile, would be the same as those that informed its decision to come to the table in 2015: to end decades of near-isolation, escape the shackles of economic sanctions, and finally build a nation that can live up to the potential of its people.

The regime might reasonably argue that Trump’s unilateral withdrawal from the Joint Comprehensive Plan of Action makes such agreements moot. That objection can best be overcome by fixing another of the old deal’s weaknesses: It was an executive agreement, rather than a formal treaty. The presidential candidates should commit to submitting any new bargain to Congress for ratification, thereby forestalling Iran’s skepticism about its durability.

Since Trump’s policies have shown no signs of working, it surely makes sense for presidential candidates to signal a renewed openness to talks with Iran. But they should also recognize that the Islamic Republic’s actions have changed the facts on the ground, making a simple return to the terms of 2015 impossible.