It is not a major foreign policy insight to say that America is better off when our closest allies believe we will stand by our agreements.

Yet President Trump is reportedly preparing to do the exact opposite by initiating, before Oct. 15, a process to blow up an internationally-negotiated nuclear agreement with Iran known as the Joint Comprehensive Plan of Action (JCPOA) by determining that the agreement is not in our national interest.

The JCPOA is about one thing: stopping the Iranian nuclear weapons program in its track. Iran agreed to it because the United States spent years lining the world up to apply suffocating economic sanctions and then led intensive negotiations to get the deal done.

As a result, Iran has dismantled its plutonium reactor, mothballed thousands of centrifuges, diluted enriched uranium, shipped nuclear materials out of the country, and submitted to the most intrusive inspections that have ever been applied in an international agreement.

Yet, the president is still considering this action even though every entity from U.S. intelligence services to the International Atomic Energy Agency (IAEA) has verified that Iran is in compliance.

A presidential determination that the agreement is not in our best interests is dangerous in multiple ways. Even senior members of President Trumps cabinet think so. Just this last week, Secretary of Defense James Mattis said he believes it is in the United States national security interest to remain in the deal.

Most importantly, a U.S. withdrawal could send Irans nuclear program back into full swing. A nuclear-armed Iran would pose an existential threat to Israel, destabilize the Middle East and contribute to an international nuclear arms race.

In addition, even if Iran didnt resume its nuclear weapons program, we would have a hard time knowing exactly what they are up to without the scores of intrusive inspections the agreement has provided. After years of trying to peer into the black box of Irans nuclear program, we finally have a window into it. Backing out of the deal would eliminate that.

Some believe that by blowing up the JCPOA, the United States would set the stage for negotiating a better deal. This is exceedingly unlikely. I have met with representatives from the European Union, the United Kingdom, Germany, and France. They all agree that Iran is in compliance with the deal and uniformly indicate they do not believe a better deal is possible and that they would not be interested in re-imposing sanctions on Iran in the false belief that it is. Without the support of the international community, including China and Russia who are also part of the agreement, Iran will not be moved to return to the table.

Moreover, backing out of the agreement to end Irans nuclear program would torpedo our efforts to secure international collaboration to end North Koreas nuclear program. Why would international partners work with us to impose sanctions on North Korea to bring them to the negotiating table, and why would North Korea come, if they know the United States does not live up to its word?

As Chairman of the Joint Chiefs of Staff Joseph Dunford stated: It makes sense to me that our holding up agreements that we have signed, unless theres a material breach, would have an impact on others willingness to sign agreements.

And more broadly, withdrawing from the deal would undermine U.S. influence in partnering with our European allies, who are critical partners on a huge range of issues. Our allies already perceive the United States as erratic and unreliable after the Presidents announcement that the U.S. would withdraw from the Paris Agreement for tackling climate disruption. This action would substantially increase that perception.

While critics cite Irans malicious activity in the Middle East and its ballistic missile program as reasons to back out of the deal, the JCPOA was never designed to address those threats. Instead of isolating ourselves by destroying the deal we have, we should work with international partners to stop Irans other bad actions. Congress recently passed additional sanctions against Iran related to its support for terrorism and missile development. The president should use that tool to address these problems, yet today, President Trump isnt implementing these new sanctions to the fullest extent possible.

The prospect of a nuclear-armed Iran might be the single biggest risk we face. According to every assessment, that risk is currently contained. Mr. President, lets keep it that way; dont walk away from the nuclear agreement.

U.S. Senator Jeff Merkley is a Democratic Senator representing Oregon, and a member of the Senate Foreign Relations Committee.