Soon after taking office, President Barack Obama promised he would work with Iran to negotiate a nuclear agreement that “will open the door to greater opportunity” not only for its people but for U.S.-Iranian relations. We were also told he would only negotiate a deal that prevented Tehran from acquiring nuclear weapons.

A deal with Iran was finalized in July 2015, but only after paving the way for Tehran to eventually have nuclear weapons—along with billions of dollars in frozen assets and a $400 million ransom payment to release American hostages. Ironically, Obama, who gave no quarter negotiating with Republicans on Obamacare, gave away the store negotiating with Iran.

Upon the first anniversary of the nuclear deal with Iran, Secretary of State John Kerry was asked how the relationship with the U.S. had benefitted.

Pressed for a responsive answer, Kerry could only offer that it enabled the U.S. to quickly negotiate the release of ten sailors on two Navy boats that ventured into Iranian waters in January of this year after one boat broke down.

Of course, Kerry failed to explain negotiations should not have even been necessary, as international maritime law mandated the Iranians provide assistance to the sailors, enabling them to continue their transit.

Instead, the Iranians humiliated the sailors, requiring them to kneel with hands behind their heads while they searched the boats and their contents, taking cell phones and computers.

What Kerry chose to see as a “win” for the U.S.-Iran relationship was clearly only a win for the mullahs.

Not only has a nuclear deal not tempered Iranian aggression towards the U.S., the mullahs have continued to live up to their role as the world’s top state sponsor of terrorism as reported by the U.S. State Department.

Additionally, despite White House claims that Iran and al-Qaeda are working together are “baseless conspiracy theories,” Obama’s Treasury Department suggests otherwise. Earlier this month, Treasury designated three senior al-Qaeda leaders, inside Iran, as terrorist funding operatives.

On August 24, Iranian patrol boats brazenly harassed a U.S. warship, the USS Nitze, while in international waters in the Persian Gulf near the Strait of Hormuz.

Four Iranian Revolutionary Guard Corps boats conducted a high-speed intercept of Nitze, with their guns uncovered. They continued their menacing approach, despite calls from the warship to turn away, the sounding of its whistle and the firing of warning flares. Two of the boats maneuvered as close as 300 yards before slowing and finally turning away.

Clearly Iran’s navy has been given free rein by the mullahs to unnecessarily and dangerously create tensions along a highly-trafficked maritime highway. Perhaps emboldened by the U.S. Navy’s January embarrassment, the mullahs seek to add another notch to their belt of international maritime transgressions.

Within 24 hours of the USS Nitze intercept, the Iranians were back at it.

On August 24, a Navy patrol craft, the USS Squall, was operating in the northern end of the Persian Gulf when a single Iranian boat approached in a similarly harassing manner. Again the U.S. vessel, by means of both radio communications and flares, endeavored to ward the Iranian off. When this failed and the Iranian closed to within 200 yards, the Squall, complying with international maritime procedures, fired three warning shots into the water to underscore its message to stay away.

Ever since late last year, Iran has embarked upon a consistent pattern of provocative maritime actions.

December 2015 saw Tehran give very short notice it would conduct a live fire exercise in the Strait of Hormuz. This is an extremely narrow chokepoint through which commercial vessels and almost a third of all the world’s oil traded by sea passes. With shipping lanes in either direction only two miles wide, plus a two-mile wide median strip between them, there is little room for error.

Yet it was here the Iranians conducted the exercise, launching their rockets, some of which came within 1,500 yards of the aircraft carrier USS Harry S. Truman.

January 2016 then started off with Iran’s capture of the ten U.S. sailors. Later that month, it flew a drone directly over the aircraft carrier USS Harry S. Truman.

In February, Iran undertook the mock sinking of a mock-up of the aircraft carrier USS Nimitz. Such an act, obviously, raises concern about the mullahs’ real intentions in sending boats out in such a menacing manner. (Could these be mock runs for the real thing?)

In May, the Iranians conducted a “catch and release” of a Marshall Islands-flagged cargo ship for which, under a security agreement, the U.S. is to provide protection. Later that month, they harassed a U.S. cargo ship transiting the Strait.

In July, as the head of Central Command, General Joseph Votel, visited the USS New Orleans operating in these waters, Iranian boats sailed dangerously close.

All these maneuvers not only endanger U.S. Navy assets, they demonstrate Iran is irrationally fearless in violating maritime law despite the potential to create an international incident.

It is ludicrous for Obama and Kerry to believe the nuclear deal with Iran has improved anything — evidenced most recently by State Department warning Americans that they risk kidnapping for ransom when traveling to Iran.

Our previous dealings with the mullahs should have taught us one thing: they only behave when the threat of force becomes a reality.

We saw this in January 1981 when our U.S. embassy hostages were released in Iran just minutes after Ronald Reagan was sworn in as president.

We saw this in April 1988 after our swift, iron-fisted response to Iran’s near-sinking of USS Samuel Roberts—attacking two oil rigs and sinking or damaging six Iranian boats.

And we saw this in March 2003, immediately following our invasion of Iraq as the mullahs feared a U.S. pivot towards Iran.

It won’t happen, but Obama should now inform Iran he is giving the U.S. Navy authority to use deadly force in the face of any future provocative threat by Tehran.

Lt. Colonel James G. Zumwalt, USMC (Ret.), is a retired Marine infantry officer who served in the Vietnam war, the U.S. invasion of Panama and the first Gulf war. He is the author of “Bare Feet, Iron Will–Stories from the Other Side of Vietnam’s Battlefields,” “Living the Juche Lie: North Korea’s Kim Dynasty” and “Doomsday: Iran–The Clock is Ticking.” He frequently writes on foreign policy and defense issues.