By Richard Goldberg and Mark Dubowitz, Newsweek: In line with a request issued Monday by 387 members of the U.S. House of Representatives, Secretary of State Mike Pompeo is preparing a diplomatic campaign to block one of the most damaging concessions enshrined by the Iran nuclear deal—namely, the lifting of the international arms embargo on Iran this coming October. Mr. Pompeo's effort merits bipartisan support at home and allied support abroad—not only to counter Iran's proxy war campaigns, but to stop Russia and China from shifting the balance of power in the Middle East.

The end of the arms embargo is one of the many key international restrictions on Iran scheduled to expire over time—the so-called "sunsets" negotiated alongside the nuclear agreement. Yet it makes little sense to lift an arms embargo on a regime that has steadily increased its violent behavior over the past year, ranging from cruise missile strikes on Saudi oil infrastructure to mine attacks on tankers in the Persian Gulf and rocket attacks on American and British forces in Iraq. Meanwhile, the regime continues to train and equip proxy forces in Lebanon, Syria, Iraq, Yemen and Gaza, all of which add to instability and civilian suffering.

Accordingly, the first phase of Pompeo's plan is to propose a new U.N. Security Council resolution to extend the arms embargo on Tehran indefinitely. Russia and China are expected to block the proposal, because the end of the embargo will unshackle their efforts to employ arms sales as a means of turning Iran into a client state.

This acceleration of great power competition is the larger story unfolding here. The Pentagon reports that Beijing and Moscow are planning to sell Iran fighter jets, main battle tanks, attack helicopters and modern naval capabilities. Tehran is likely to proliferate some of this advanced weaponry to the likes of Lebanese Hezbollah, Shiite militias in Iraq, Hamas and Islamic Jihad in Gaza, and the Houthis in Yemen.

Iran is already a customer for Russian nuclear power plants and air defense. China has long been the source of Iran's most proliferation-sensitive materials and is the last paying customer for Iranian crude oil exports. They have been eagerly awaiting the end of the embargo.

Phase two of Pompeo's plan circumvents Russian and Chinese obstruction. He intends to use the self-destruct—or "snapback"—mechanism of the nuclear deal to block the sunset of the arms embargo, removing the need for an extension.

This mechanism gave all original parties to the nuclear deal—including the U.S.—the right to snap all U.N. sanctions and embargoes back into place if the Iranian regime ever breached its nuclear commitments. Such breaches are now indisputable. The International Atomic Energy Agency reported in March that Iran has tripled its production of enriched uranium since November and is denying nuclear inspectors access to suspicious sites.

Even though the Trump administration withdrew from the nuclear deal, it retains the right to initiate a snapback. Specifically, U.N. Security Council Resolution 2231, which put the U.N. imprimatur on the nuclear deal, defines the term "participant State" to include the United States. According to a State Department legal opinion, Resolution 2231 does not contemplate a change in that definition even if America ceases participating in the agreement. This was not an accident, but a rare case of foresight on the part of the nuclear deal's negotiators. Indeed, the Obama administration heavily marketed this unconditional snapback prerogative as a key feature of the deal in 2015.

Unsurprisingly, Russia and China object to this interpretation. They are hoping Europe will persuade Washington to relent. London, Paris and Berlin readily acknowledge the flaws of the nuclear deal, especially its sunsets, but they remain wedded to the belief that engagement on any terms can empower purported moderates and divert Tehran from its decades-long quest for nuclear weapons capabilities.

With the first nuclear deal sunset now on the horizon, European leaders face an important choice. They have an opportunity to show that they understand great power competition is becoming the most important dynamic in the Middle East. By supporting snapback, they can deny strategic victories to Russia and China while blocking the Iranian regime's access to dangerous weapons.

The Trump administration has made clear that snapback is inevitable. The only question remaining is whether supporters of the Iran nuclear deal in America and Europe can let go of an agreement nearing the end of its shelf-life in support of overriding shared strategic objectives.

Richard Goldberg, who served in the Trump National Security Council, is a senior advisor at the Foundation for Defense of Democracies, where Mark Dubowitz is chief executive officer.