Dan Sullivan, a Republican, represents Alaska in the Senate.

As a candidate, Donald Trump said he would “tear up” the Iran nuclear deal once elected. Many of us in the Senate strongly opposed this deal on substance — it provides the world’s largest state sponsor of terrorism a pathway toward nuclear weapons inside of a decade — and also on process. The Obama administration sought the approval of the U.N. Security Council, but essentially ignored the constitutional role of the Senate in seeking to finalize the deal as an executive agreement, not a treaty. As a result, President Trump would be within his rights and authority to undo the deal through executive action, particularly as Iran continued to show that it has no intention of abiding by the deal by launching yet another ballistic missile on Sunday.

But there is a potentially better alternative than unilaterally disavowing the deal: Let it fail on its own by vigorously enforcing it.

Since the enactment in 2015 of the Joint Comprehensive Plan of Action (JCPOA), the United States, China, France, Russia, Britain and Germany, known as the P5+1, have, for their own political and economic reasons, studiously looked the other way as at least four key provisions of the deal have been violated.

First, Annex 1 of the JCPOA limits Iran’s stock of heavy water — a catalyst for nuclear weapons. According to the International Atomic Energy Agency, there are at least two instances of Iran knowingly exceeding its heavy water limit — in February and November of last year. Instead of holding Iran to account for the violations, the Obama administration bought up the illicit material for $8.6 million.

Second, Annex B of U.N Security Council Resolution 2231 — which serves as the implementing resolution for the JCPOA and its legal framework — calls on Iran not to undertake any “activity related to ballistic missiles” for eight years. However, Iran has conducted five ballistic missile tests since the deal was finalized.

Third, Annex B of the implementing resolution also bans certain individuals from travel to foreign countries. Yet nothing was done when it was discovered that Iran’s Quds Force commander, Qasem Soleimani, who is on that list, traveled to Russia to meet with President Vladimir Putin after the deal was signed. As recently as December, Soleimani was seen visiting Aleppo.

Finally, Annex B also states that the Security Council must approve “services, advice, other services or assistance,” related to the sale of conventional weapons. It’s been widely reported that Russia is in talks to sell Iran $10 billion worth of conventional weapons, including advanced tanks, artillery systems, planes and helicopters. Iran has not asked for such approval.

(Reuters)

No member of the P5+1 has done anything about these violations. Russia is complicit in them; China needs Iran’s oil and gas; Europe wants business deals; and the Obama administration didn’t want to undermine what it saw as a major foreign policy legacy.

But Trump’s interest is in protecting Americans and our allies in the Middle East. And that could be done by stating that the United States will abide by the terms of the deal, while also making clear that those terms are already being systematically violated. He could give all the parties to the agreement 60 days to remedy the situation. If they fail to do so, he should take the next step, pursuant to the agreement: reapply sanctions against Iran.

The conventional wisdom, as spun by the Obama administration officials who negotiated this ill-advised deal, is that only a re-imposition of sanctions by the entire “international community” would be effective against Iran. But, as so often was the case in 2016, the conventional wisdom is wrong. Even unilateral U.S. sanctions could be significantly destabilizing to the Iranian regime and its economy.

I’ve seen this work first hand. As an assistant secretary of state in charge of economics, energy, terrorist finance and sanctions during President George W. Bush’s second term, I served with other senior members of the State and Treasury departments to encourage allies and businesses around the world to quit doing business with Iran or risk secondary sanctions from the U.S. Congress.

Working with Congress, both the Bush and Obama administrations were able to impose sanctions that targeted states and individuals who conduct business with Iran’s central bank. We also were able to ensure significant restriction of Iranian access to the U.S. financial system, including those that are conducted in dollars, which need to be cleared through a U.S. financial institution, even if the money isn’t staying in the United States. We also encouraged countries and companies to divest from the Iranian oil and gas sector.

Many of our allies only reluctantly agreed to economically isolate Iran, largely due to this pressure.

Even acting unilaterally, we still have leverage to put pressure on Iran and the international community to yield results. Our power over the international financial system remains, and with regard to energy, U.S. leverage has increased dramatically. The United States is once again the world’s energy superpower. As such, we could give countries and companies a choice: Invest in Iran’s oil and gas sector or invest in America’s. I believe that most companies would choose the United States.

With strong, principled U.S. leadership, others countries will follow. If they don’t, the Trump administration will be able to say that the United States abided by the spirit and letter of the agreement, and it was the other members of the P5+1 who chose to turn a blind eye to Iran’s violations and walk away from the deal.