Editor’s Note: The National Interest and the Heritage Foundation have partnered for a multi-part occasional series examining various aspects of the Iran nuclear agreement. The below is part four of the series. You can read previous parts here: one, two and three.

Last summer’s Iran nuclear deal has been roundly criticized for a number of solid reasons, ranging from Tehran’s ability under the deal to continue advanced centrifuge research to lingering questions about the possible military dimensions of its nuclear program.

That’s all well established.

One issue that has been largely ignored—wittingly or unwittingly—is this: What if Iran were able to find a suitable partner to collude with on a ‘‘underground” nuclear weapons program, all while seemingly staying within the restrictions of the July 2015 nuclear deal?

In other words, Tehran could by all public accounts adhere to the P5+1’s (China, France, Germany/European Union, Russia, the United Kingdom and the United States) Joint Comprehensive Plan of Action (JCPOA). But concurrently, Iran could work clandestinely with another country to advance its nuclear weapons program, essentially circumventing the International Atomic Energy Agency’s inspections and monitoring of the nuclear program inside Iran.

What better candidate for covert cooperation than cagey North Korea?

First, there’s no doubt that North Korea has a nuclear weapons capability. It has conducted four—maybe soon five—tests (2006, 2009, 2013 and 2016), possibly using both plutonium and uranium as fissile material.

Next, some analysts believe Pyongyang may have already “miniaturized” or “weaponized” the underground testing device into a nuclear warhead, capable of being mated to a ballistic missile. Even if North Korea hasn’t achieved it yet, it’s working on it.

Pyongyang has also expanded its missile testing beyond land-based launches. It now has conducted at least two subsurface ballistic missile tests that may also be related eventually to its nuclear weapons program. Clearly, these North Korean capabilities—though not all proven—would benefit an Iranian nuclear weapons program.

Also important is that Pyongyang seems willing to share its nuclear know-how with others, as evidenced by its building of a nuclear facility for Damascus that was destroyed in an Israeli air strike in 2007. Though public evidence is scarce and, if available, gauzy, it’s quite reasonable to conclude with some confidence that Pyongyang and Tehran already have some sort of established security or defense relationship. For instance, in 2012, Iran and North Korea reportedly signed a science and technology (S&T) agreement. It’s fair to assume that any cooperation is defense-related.

Indeed, considering the sorry state of their respective economies, research and industrial bases, it’s hard to conceive of what sort of civilian S&T Pyongyang might offer Tehran—and vice versa, of course.

Lending credence to this idea is the report that, at the time of the S&T agreement’s signing, Iran’s Supreme Leader, Ayatollah Ali Khamenei, spoke of how Tehran and Pyongyang had “common enemies.” The United States quickly—and clearly—comes to mind.

The idea of collaboration should come as no real surprise, as it’s seemingly well-known that the Iran and North Korea are reported to have been cooperating at some level on ballistic missiles going back to at least the late 1990s. For instance, it’s long been asserted that some Iranian ballistic missiles (e.g., the Shahab) are based on North Korean ballistic-missile technology (e.g., the Nodong) or transfers (e.g., the Scud).

Equally alarming is the New York Times report suggesting that the 2013 North Korean nuclear test may have been conducted “for two countries.” That notion was raised by unattributed U.S. government sources and gives support to concerns that Pyongyang and Tehran may be cooperating on more than ballistic missiles. This wouldn’t be the first time such an allegation has been leveled at Tehran and Pyongyang informally, but perhaps the first time it’s been acknowledged by Washington, taking into account a source not willing to be identified.

Of course, the situation has changed dramatically with the JCPOA now in force. Iran now has more than a passing interest in moving forward with its nuclear weapons program—especially considering the evolving regional security situation—without losing the benefits that the agreement provides, such as the removing of crippling economic sanctions. From Iran’s perspective, the need for “nuclear networking” with North Korea is greater than ever.

Of course, it’s not just Tehran that is in need. Pyongyang is also needy for its own reasons, such as its self-imposed, collectivist economic woes and the increasing international economic sanctions it faces over nuclear and missile tests.

In addition, North Korea could use some technical assistance with its space launch program, where Iran is arguably more advanced, but which is integral—and critical—to Pyongyang’s intercontinental ballistic missile (ICBM) program.

Lastly, both countries despise the United States and some of its allies (e.g., South Korea and Israel). Accordingly, Iran and North Korea would benefit from the existence of another state that threatens America with nuclear-tipped ICBMs.

In other words, there’s plenty of political and military motivation for these two rogue states to get together on nuclear and/or missile matters, arguably even more so today than last summer, before the JCPOA came into effect.

Peter Brookes is a Heritage Foundation senior fellow and a former deputy assistant secretary of defense. Follow him on Twitter: @Brookes_Peter.

Image: Wikimedia Commons/Khamenei.ir