If President Donald Trump decertifies the Iran nuclear deal under law because, in his determination, quoting the law, “suspension of sanctions related to Iran” is no longer “appropriate and proportionate to the specific and verifiable measures taken by Iran with respect to terminating its illicit nuclear program; and… vital to the national security interests of the United States…” then he cannot afford to send a mixed message. He has to go the full nine yards and reinstate sanctions on Iran, too.

To be clear, the legislation that enacted the Iran nuclear agreement in 2015 authorized the sanctions to be “waived, suspended, reduced, or otherwise relieved” by then President Barack Obama. The underlying statutes that authorized prior president to originally implement the sanctions remain in effect.

Meaning, President Trump already has all the authority from Congress he needs to reinstate the sanctions.

There is no particular need for Congress to revisit the issue, an option reportedly under consideration. Under the Iran nuclear deal, in the event the President does not recertify the agreement, Congress has 60 days to act to consider reinstating sanctions.

But that is only one option.

The fact is, Congress has already acted.

For example, the Iran Sanctions Act that covered nuclear activities, the oil industry and other areas — waived under the Iran nuclear deal — was set to itself expire on Dec. 31, 2016. But Congress reauthorized it after the 2016 election, with the sunset extending to Dec. 31, 2026. Although these particular sanctions remain waived pursuant to the Iran nuclear deal, the purpose of the reauthorization was so the Trump administration and other future administrations would have the option of scrapping the Iran nuclear deal if necessary and reinstating all of the prior sanctions.

Similarly, Section 1245 of the 2012 National Defense Authorization Act, authorizing the President to freeze financial assets of Iran and those doing business with Iran as well as sanctions against Iran’s central bank, remains in effect. It has only been waived under the Iran nuclear deal. But if Trump decertifies the agreement, he can reinstate it. Congress doesn’t have to do a thing.

The same stands for the 2013 Iran Freedom and Counter-Proliferation Act (Subtitle D of the 2013 National Defense Authorization Act) and the 2012 Iran Threat Reduction and Syria Human Rights Act. All remain in effect and were merely waived by President Obama pursuant to the Congressionally enacted Iran nuclear deal in 2015.

Trump could also unilaterally reinstate Executive Orders 13574, 13590, 13622, 13645, and Sections 5-7 and 15 of Executive Order 13628, again, without Congress.

All of these prior sanctions were well within the President’s Article II constitutional authority to conduct foreign relations and found explicit backing in the aforementioned statutes and in other statutes as well, including the International Emergency Economic Powers Act (50 U.S.C. 1701 et seq.) (IEEPA), the National Emergencies Act (50 U.S.C. 1601 et  seq.),  the Comprehensive Iran Sanctions, Accountability, and  Divestment  Act  of  2010  (Public Law 111–195) (22  U.S.C.  8501 et seq.), as amended (CISADA), and section 212(f) of the Immigration and Nationality Act of 1952 (8 U.S.C. 1182(f)).

None of the above-mentioned laws were ever repealed by the Iran nuclear agreement. All Congress authorized the President to do was “suspend, waive, reduce or otherwise relieve” the sanctions.

Now, surely Trump can and should consult with members of Congress about which sanctions to reinstate, but he does not need their permission, which has already been granted. At the end of day, it is Trump who is the President of the United States.

This is not the same as kicking Deferred Action of Childhood Arrivals (DACA) down the road for six months for Congress to consider as part of wider considerations on, say, the RAISE Act ending chain migration, beefing up border security and building the wall, items that might be negotiated.

These are sanctions to curtail Iran from becoming the next North Korea, a rogue regime with nuclear weapons threatening to use them. If Trump is going to decertify the current agreement with Iran, because of noncompliance with it and Iran’s obligations under the Nuclear Non-Proliferation Treaty, because it turns out Iran is still on a crash course to build nuclear weapons, then there can be no ambiguity. The agreement should be decertified — and the sanctions put back into effect.

Another note on going back to Congress. In every case of the aforementioned sanctions, Congress has delegated authority to the President, some going back decades, to implement official, full force of law sanctions so that he can act quickly, and decisively. This is by design. The President is at the height of his powers when he acts with Congressional backing.

In that sense, if Trump wants to scrap the Iran nuclear deal because he determines that Iran’s continued pursuit of nuclear weapons is a threat to national security, then he not only has the Congressional authority to act but a duty to act on behalf of the American people.

This is not a political football to punt to Congress.

There can be no half measure, which risks being viewed as a sign of weakness. For example, if Trump were to decertify the Iran nuclear deal, but not reinstate sanctions, the risk is of Congressional inaction on a matter of vital importance. Instead, if there must be any debate in Congress, it should only be on strengthening a reinstated sanction regime.

The bottom line is that there is little reason to decertify the Iran nuclear deal unless the intent is to reinstate the sanctions. And leaving it up to this Congress to do the right thing could be a big mistake. Particularly when the goal should be to put pressure on Iran.

This is the reason under the Constitution that there is only one president. So that in matters of foreign affairs, we speak with one voice.

At the end of the day, having the hapless House and Senate debate whether Iran ever broke the deal or not will hardly be a show of strength. It might even send an unintended message of political division over U.S. intent to disarm Iran’s nuclear weapons program. Remember, Mr. President, weakness is provocative.

Robert Romano is the Vice President of Public Policy at Americans for Limited Government.