This post is part of an ongoing series preparing for the AEI/CNN/Heritage National Security & Foreign Policy GOP presidential debate on November 22.

Engagement with Iran was Barack Obama’s signature foreign policy issue. During the Democratic primaries, Obama promised to meet the leaders of Iran “without preconditions.” Less than a week after taking office, Obama told al-Arabiya’s satellite network, “If countries like Iran are willing to unclench their fist, they will find an extended hand from us.” Obama subsequently sent Iran’s supreme leader two letters seeking dialogue.

Iran’s leadership dismissed all of Obama’s entreaties out of hand. When Obama waived preconditions, Supreme Leader Khamenei and President Ahmadinejad asserted their own, not the least of which was an American withdrawal from the Persian Gulf. When the United States suggested opening an American diplomat-staffed visa office in Tehran, Iran’s leadership said no. When the American Navy sought a hotline to defuse any crisis in the Persian Gulf, the Iranian government said that if the United States just left the region, then there would be no chance of a crisis.

Nothing Obama did was new. Every president since Carter has tried to engage the Islamic Republic diplomatically. Carter had sent letters, which were returned. Reagan had sought to negotiate over American hostages. Like Obama, the elder George Bush had extended an olive branch during his inaugural speech. Clinton became entranced with reformist President Mohammad Khatami’s call for a “Dialogue of Civilizations.” George W. Bush repeatedly allowed his diplomats to sit down with their Iranian counterparts.

The track record for their diplomacy is poor: Iran remains the largest state-sponsor of terrorism, its ballistic missile program has expanded to the brink of intercontinental capability, and the regime appears to be on the brink of break-out nuclear weapons capability. The reformists upon whom the White House pins its hopes argue with their hardline rivals not about whether Iran’s nuclear capability is right or wrong, but rather who deserves credit for advancing it so far. Khatami’s aides have gone so far as to brag that they duped the West with their dialogue of civilizations rhetoric.

Because neither diplomacy nor narrowly constructed sanctions have worked, it might be useful for the next occupant of the Oval Office to consider what has: In 1981, after years of fruitless diplomacy, Khomeini suddenly agreed to release American hostages. The reason was not some new diplomatic initiative, but rather the outbreak of war with Iraq: Suddenly, the cost of Iran’s isolation had become too great to bear.

After two years, the Iranian military finally pushed back the Iraqi invasion; Khomeini swore Iran would keep up the fight until Iraqi dictator Saddam Hussein fell. There followed six years of stalemate. In 1988, with Iran’s economy decimated and a generation lost, Khomeini finally reversed course. Declaring his decision like drinking a chalice of poison, he agreed to a ceasefire. The cost of pursuing his revolutionary policy had simply become too great to bear.

If the next administration aims to force Tehran to reconsider its pursuit of nuclear weapons, it must raise the cost of Iran’s nuclear program beyond the breaking point. Any serious candidate should explain which strategies they will employ not only to bring Iran to the table, but to raise the cost of defiance beyond Tehran’s tolerance.

Michael Rubin is a resident scholar at AEI