Former secretary of state John Kerry warned Tuesday that if the United States withdraws from the Iran nuclear deal, it will take decades to re-negotiate another set of limitations on Tehran’s nuclear program

Speaking to the World Affairs Council at Villanova University in suburban Philadelphia, Kerry recalled the atmosphere of deep distrust surrounding the talks, particularly between the two countries with a long history of enmity. Iran’s Supreme Leader Ali Khamenei repeatedly told his envoys they could never trust the United States. Kerry said U.S. allies in the Middle East were urging the Obama administration to bomb Iran, not talk with it.

Despite the pressure, six world powers eventually agreed to lift sanctions and Iran agreed to open up its nuclear facilities to international monitors and abide by curbs on its enriched uranium. Kerry called it the “strictest, most transparent, most accountable arms control agreement on the planet today.”

“If we pull back from what they have done, it will be 30 years before another president will ever sit down with Iranians to negotiate,” said Kerry, who was involved in secret meetings that kickstarted negotiations and then often led them. “Then we will be on track, if something goes wrong, of confrontation.”

President Trump has indicated he is inclined to take steps in May that could kill the 2015 agreement, although U.S. officials have been meeting with Europeans to see if they can find ways to address Trump’s concerns. Kerry suggested Iran would likely take immediate steps to enrich more uranium and other actions now prohibited until the limits “sunset,” in some cases 15 years in the future.

“Why would anyone want to leap ahead 15 years, and make it happen now?” Kerry asked.

Kerry, who has been immersed in writing his autobiography since leaving office 14 months ago, has made few public remarks as the efforts he cared most about have been eviscerated or cast aside by the Trump administration. Chief among them are the Iran deal, the Paris climate accord and the Trans-Pacific Partnership, a trade agreement.

Now, he is starting to take his criticism of Trump and his policies, into the open.

“Instead of responding to obvious needs, we see self, party and ideological interests trumping — no pun intended — the real interests of our nation,” he said.

Later, Kerry said previous generations of Americans had leaders “who actually stood up and led.”

“Today we don’t see that,” he added. “We get early morning tweet storms. Diversions from reality, from the truth itself.

“What I see today is a shocking avoidance of reality.”

Kerry talked briefly about Russian interference in the 2016 election, saying he suspected Russian President Vladimir Putin’s dislike for Hillary Clinton began when she gave a speech comparing him to Hitler.

Kerry said he found it necessary to “compartmentalize” criticism of some Kremlin actions so they could work together on issues of mutual concern. Making progress with the Syrian government that is led by President Bashar al-Assad, he said, depends on Russia’s cooperation.

“There is no solution to Syria without Russia, and without Iran,” he said. “They went in. We didn’t. They’re there. We’re not. They have influence with Assad. We don’t.”

In a casual aside, Kerry said what he missed most about being secretary of state was the ability to initiate events and groups to work on pressing world problems. At the end of the evening, Kerry had to rush to Philadelphia’s 30th Street Station to catch a train home.