By refusing to certify Iran’s compliance with the multilateral nuclear deal, President Donald Trump is evading his responsibility under a law adopted by Congress. His action will accomplish nothing and may cause great harm.

The certification is a procedure under the Iran Nuclear Review Act of 2015. The law was adopted by Congress to require the president to certify, every 90 days, that Iran is complying with the 2015 Joint Comprehensive Plan of Action, which subjects Iran’s nuclear program to limitations and special inspection in return for lifting sanctions that were in place against Iran at the time.

As specified by the Iran Nuclear Review Act, certification is to relate to Iran’s compliance. The president is to certify that the suspension of anti-Iran sanctions remains “appropriate and proportionate to the specific and verifiable measures taken by Iran with respect to terminating its illicit nuclear program.”

Under a side document to the Plan of Action, monitoring is done by the International Atomic Energy Agency.

On Aug. 31, that agency reported it has been able to monitor and has found no deviation by Iran. Trump’s Cabinet secretaries agree that Iran is complying. So does Trump alter-ego Nikki Haley, our ambassador at the United Nations.

Trump himself does not contest that Iran is complying. Trump has declined to certify on the basis of issues wholly outside the Plan of Action, prominently, Iran’s recent testing of ballistic missiles and its support for various elements in the broader Middle East picture that Trump characterizes as terrorist. A memo to the White House: Iran is fighting against the Islamic State in both Syria and Iraq.

Congress should tell Trump that his refusal to certify is invalid because he is raising extraneous issues. Congress should ignore Trump’s action.

But the Republicans in Congress are trying to come up with revisions to the Plan of Action, in particular, to amend its so-called “sunset” provisions on various of Iran’s obligations so that the plan will bind Iran longer.

This effort is a nonstarter even if this famously dysfunctional Congress can find language for a revised Plan of Action on which it can agree.

The Plan of Action is not simply between Iran and the United States. It involves Iran on one side, and on the other the European Union plus France, Germany, Britain, Russia, China and the United States.

The other parties on our side have said they will not ask Iran to renegotiate. And Iranian President Hassan Rouhani has refused to negotiate. So any proposal Congress devises to redo the Plan of Action it will be a dead letter.

The judgment of the countries that joined with us and with Iran in fashioning the Joint Comprehensive Plan of Action was that dragging other issues into the mix would complicate an already complex negotiation and, in effect, doom it.

By his noncertification, Trump has turned public opinion in Iran sharply against the United States and has driven President Rouhani into the arms of the less-moderate elements in Iran who opposed any nuclear deal as an assault on Iran’s sovereignty. In the longer term there is little prospect of benefit.

Iran has said all along that its nuclear program is like those of many countries, aimed at production of power for peaceful purposes. It denies it was trying to build nuclear weapons.

Whether it was may never be known. But the Joint Comprehensive Plan of Action called for inspections that are more intrusive than the inspections required under the Nuclear Non-Proliferation Treaty.

For now, the Plan of Action is being observed by all parties, including the United States, and sanctions remain lifted. Hopefully President Trump will find this act of noncertifying a sufficient show of displeasure and will leave things as they are.

John B. Quigley is a distinguished professor of law at Ohio State University. He is the author of 11 books on various aspects of international law. Readers may write to him at Moritz College of Law, 55 W. 12th St., Columbus, Ohio, 43210.