The anniversary of the bombing should serve as a stark reminder that the Iranian regime will probe for vulnerabilities and punish America if we are not strong, and that the costs to America from Iranian malign activity can be enormous. We should never forget that day, and we should never appease Iran’s terrorist leaders.

The Middle East has changed a great deal since 1996. Israel has been recognized by many majority-Muslim states as part of the Abraham Accords. But the government of the Islamic Republic of Iran remains as committed to carrying out terrorism today as it was a quarter-century ago.

Iran’s responsibility for Khobar is indisputable. In a 2001 federal indictment of Saudi Hizballah members involved in the attack, the Justice Department found that “elements of the Iranian government inspired, supported, and supervised members of the Saudi Hizballah.” In 2006, in a lawsuit brought by families of 17 victims of the bombing, a federal judge ruled that Iran was responsible for the attack: “The totality of the evidence at trial . . . firmly establishes that the Khobar Towers bombing was planned, funded and sponsored by senior leadership in the government of the Islamic Republic of Iran.” Another federal judge last year ordered Iran to pay nearly $900 million to victims and their families for its culpability.

Orchestrating the death and maiming of Americans is a day at the office for the mullahs who run the Islamic Republic. Since seizing power by force in 1979, the regime has consistently targeted U.S. military personnel across the Middle East. In 1983, Iran worked with an early incarnation of Hezbollah to kill 241 American service members by bombing their barracks in Beirut, Lebanon. In that attack, the Khobar Towers bombing and others, Iran has enlisted terror groups to do its dirty work. Iran’s Quds Force, the wing of the Islamic Revolutionary Guard Corps assigned the task of spreading the Islamic Revolution via military engagement, used this strategy to great effect during the Iraq war. Iran helped kill more than 600 American troops during that conflict through terror groups like Kataib Hezbollah. These loose associations allow the Iranian regime to deny its role in terrorist attacks—denials only the most gullible can believe.

Foolishly, the Obama administration tried to appease Iran into good behavior by agreeing to the nuclear deal in 2015. At the core of this misguided diplomacy was the notion that Western engagement and trade with Iran would transform an outlaw regime into a constructive actor in the Middle East. Instead, Iran took advantage of the economic windfall from the removal of sanctions to increase funding for Shiite proxy militias across the region, with many of them taking orders from Quds Force head thug Qasem Soleimani. He was actively plotting new attacks against American soldiers and diplomats in the Middle East when the Trump administration took him off the battlefield in January 2020.

Now the Biden administration is about to empower the world’s foremost state sponsor of terrorism again. The president is racing to repeal sanctions and rejoin the Joint Comprehensive Plan of Action, an agreement that would give the ayatollahs a greater ability to underwrite terrorist attacks like the Khobar Towers bombing and the recent barrage of Hamas rockets that would have taken countless Israeli lives had the Iron Dome interceptor system not worked to near-perfection. President Biden has learned nothing from Tehran’s behavior over the past 40 years.

Nothing will change under incoming Iranian President Ebrahim Raisi, who won a rigged election and is a close ally of Supreme Leader Ayatollah Khamenei. I was proud to help drive sanctions against him in 2019 for grotesque human-rights violations.

The Trump administration wasn’t fooled about the nature of the Iranian regime, or how the nuclear deal exposed Americans to greater harm. So we pulled out of it and slapped more than 1,000 sanctions on Iranian entities. We re-established military deterrence against Iran. We supported Israeli security more than any other U.S. administration in history, both bilaterally and through the Abraham Accords. Our actions reduced the operational and financial capacity for terror by groups like Hezbollah in Lebanon and various Shiite militias in Iraq.

We confronted Iranian aggression. Mr. Biden is encouraging it.

The Khobar Towers bombing caused immense heartache for American families who saw the lives of their husbands, fathers, brothers and sons cut short in the name of Iran’s Islamic Revolution. Mr. Biden and his team risk the recurrence of this type of bloodshed if they fail to recognize that rejoining the deal will aid Tehran’s decadeslong campaign of killing Americans.

Mr. Pompeo is a distinguished fellow at the Hudson Institute. He served as secretary of state, 2018-21.