“This deal is not based on trust,” President Obama said when he announced in July that a nuclear accord had been negotiated with Iran. “It’s based on verification.” Obama had said the same thing in April, when the accord’s “framework” was first made public, and he repeated it in August, when he defended the deal in an address at American University.

Secretary of State John Kerry, anxious to dispel concerns that duplicitous Iranian theocrats bent on acquiring nuclear warheads would be able to hoodwink their Western interlocutors, put the point even more strongly.

“There’s nothing built on trust,” Kerry insisted to CBS. “You don’t have to trust the people you’re dealing with. You have to have a mechanism put in place whereby you know exactly what you’re getting and you know exactly what they’re doing.”

No one, said Kerry, is expecting Iran to “turn over a new leaf.” Which is just as well, because Iran has no intention of changing.

On Oct. 12, the regime announced that Washington Post reporter Jason Rezaian, after more than a year in detention, had been convicted of espionage. One day earlier, Iran test-fired a new intercontinental missile, a flat-out violation of Security Council Resolution 1929. The country’s supreme ruler, Ayatollah Ali Khamenei, threatened to abrogate the nuclear deal if there is any attempt to enforce sanctions against Iran on any “pretext,” including terrorism and human rights. And as the month ended, former Iranian president Hashemi Rafsanjani conceded in an interview with Iran’s state-run news agency that the country’s nuclear program was indeed first cooked up as a means to create a nuclear deterrent.

So, no, Iran is not about to turn over a new leaf. It remains as hostile and belligerent as ever. Good thing, then, that Obama and Kerry made sure their nuclear deal was “based on verification.”

Except that verification depends on intelligence. And when it comes to flushing out clandestine nuclear activity by hostile regimes, US intelligence services have compiled an almost unrelieved record of failure.

Under the terms of the nuclear agreement, the burden of verifying Tehran’s compliance falls on the International Atomic Energy Agency, or IAEA. But for the IAEA’s inspectors to do their job, they need reliable information and ready access to the people and documents that can supply that information. As Reuel Marc Gerecht, a former case officer in the CIA’s Clandestine Service, observed in an essay last July, IAEA staffers are highly skilled at “static surveillance” — i.e., monitoring known sites where they are free to come and go unimpeded. That was the case, for example, in Libya, when the late dictator Muammar Qaddafi, alarmed by George W. Bush’s overthrow of Saddam Hussein and fearing he might be next, abruptly agreed in 2003 to surrender his entire nuclear-weapons infrastructure. IAEA inspectors, granted unfettered access to Libya’s facilities, were able to swiftly remove Qaddafi’s nuclear components and verify that the threat had been neutralized.

Unfortunately, “the IAEA’s efficiency declines in direct proportion to the deceptive hostility of the host country,” Gerecht writes. Iran has outwitted weapons inspectors for years and even now refuses to divulge, as required, the possible military aspects of its nuclear program. “We can be certain it will continue to treat the IAEA with deceptive animus, as it has since the mullahs’ clandestine nuclear handiwork was revealed by an Iranian opposition group in 2002.”

Most of what the West knows about Iran’s nuclear ambitions has not been ferreted out by deep-cover agents operating inside the country. It has been supplied by defectors and dissidents. The United States knew nothing about the Iranian nuclear facilities at Arak and Natanz, for example, until Iranian exiles revealed their existence in 2002. It was years before the United States discovered that Iran had constructed a secret enrichment operation called Fordow inside a mountain bunker near the city of Qom.

“The truth,” Gerecht concludes, “is that the CIA and the [National Security Agency] are largely flying blind inside the Islamic Republic.”

Time and time again, the United States has been caught flatfooted by dangerous nuclear advances of other governments.

The CIA was badly surprised when the Soviets tested their first nuclear bomb in 1949 and was caught unawares when India and Pakistan joined the nuclear club in 1998. America’s intelligence community severely underestimated Saddam’s nuclear progress before the first Gulf War and badly overestimated his stock of weapons of mass destruction — a “slam-dunk,” CIA Director George Tenet famously called it — on the eve of the 2003 war.

In 2005, the bipartisan Robb-Silberman commission — formed to examine the grievously flawed estimates of Iraqi WMDs — issued its devastating findings. “Across the board,” the commission reported, “the intelligence community knows disturbingly little about the nuclear programs of many of the world’s most dangerous actors.”

The blunders and blind spots haven’t been limited to nukes. The CIA didn’t anticipate the invasion of South Korea in 1950, the Soviet missile emplacement in Cuba in 1962, the Iranian revolution in 1979, or Iraq’s invasion of Kuwait in 1990. For that matter, US intelligence services were stunned by the attack on Pearl Harbor in 1941. And by the 9/11 hijackings six decades later.

It is all well and good to claim that the nuclear deal with Iran is “based on verification.” But verification works only when intelligence works — and when a regime isn’t trying to cheat. Iran has been cheating for years, and not even Obama and Kerry pretend that the mullahs have turned over a new leaf.

Jeff Jacoby is a columnist for The Boston Globe.