While details remain sketchy about the incident, Iranian patrol craft forcibly stopped and boarded a merchant ship under flag of the Marshall Islands. The incident raises two questions—what triggered it and what, if any, responsibility the U.S. may have, under its treaty with the Marshall Islands, to respond to this act of Iranian aggression.

What is known is that on April 28, the container ship Maersk Tigris was transiting north in the Strait of Hormuz, between the Persian Gulf and the Gulf of Oman in the Arabian Sea. It was headed for the port of Jebel Ali, located southwest of Dubai in the United Arab Emirates when the Iranian patrol boats approached.

The Tigris was ordered to undertake a course change that would cause it to enter deeper into Iranian territorial waters. (While the Strait of Hormuz lies inside Iran’s territorial waters, ships regularly transit it as an openly recognized international shipping lane under the principle of “innocent passage.”)

When the ship’s master refused to alter course, the boats fired a shot across the ship’s bow. The unarmed Tigris immediately sent out a distress call before stopping and being boarded by the Iranians.

The U.S. Navy destroyer Farragut was dispatched in response to the distress call and ordered to locate Tigris. However, by the time Farragut arrived near the location, the Iranians had already led the merchant ship deeper into Iranian waters, near Larak Island. Tigris is now in the Iranian port of Bandar Abbas. No Americans are known to be among the 30-plus crewmembers.

There seems to be a dispute as to whether, while transiting through Iranian waters, Tigris was on the internationally recognized shipping lane course or had veered off. Defense experts who tracked the transit support the former.

The Iranian navy has historically had navigational problems while seeking to create international incidents. In March 2007, fifteen British sailors and marines were patrolling Shatt al Arab—a long disputed waterway between Iraq and Iran—when they were seized by the Iranian navy. Claiming the Brits were in their territorial waters, the Iranians initially provided coordinates squarely putting the alleged trespassers on the Iraqi side. After the Brits pointed this out, the Iranians “re-calculated” the position, providing coordinates inside Iranian waters.

Iran’s motivation for this 2007 international incident was to draw attention away from its nuclear arms program. Undoubtedly, political motivation is again at play. As a nation state unable to act as a responsible member of the international community, Iran leaves us hard-pressed to understand its exact motivation for this action. We are left to ponder whether this, again, is an effort to take the focus off nuclear issues or, this time, to placate Tehran’s hardliners in the aftermath of Iran’s embarrassment in losing a face-off with U.S. warships that prevented an Iranian convoy from delivering war materials to Yemeni rebels a week earlier.

But, regardless of motivation, the remaining issue is what responsibilities this act of aggression by the Iranians triggers on the part of the U.S. based on its 1986 treaty with the Marshall Islands.

The U.S. took administrative control over the Marshall Islands following Japan’s defeat in 1945. When the Islands became independent in 1986, a treaty with the U.S., known as the Compact of Free Association, became effective, amended in 2004. The U.S. became responsible for the national security and defense of the Marshall Islands which, in turn, agreed not to undertake acts incompatible with those responsibilities.

Thus, it is clear the U.S. is required to act on behalf of the defenseless Marshall Islands. But, apparently, Obama’s Pentagon is rejecting President Teddy Roosevelt’s policy to “speak softly and carry a big stick” in order to “say nothing and carry no stick” as it believes otherwise.

As CBS News reports, “Pentagon lawyers have determined US has no obligation to come to the defense of a Marshall Islands-flagged vessel at sea.”

The Charge d’Affairs for the Marshall Islands Embassy in Washington, Junior Aini, disagrees with the Pentagon lawyers. He made clear the only option for his country is for the U.S. to act as required by the treaty.

This brings yet another possible motivation for Iran’s action.

In two weeks, Obama is to meet with regional Middle East leaders to let them know the U.S. will not abandon them. The mullahs may well see this incident as an opportunity to totally undermine Obama’s effort by showing he will not even act to protect the Marshall Islands’ security interests.

This action by the Iranians serves to “throw down the gauntlet” as it directly challenges Obama’s declared mission of the U.S. warships sent last week to patrol off of Yemen. As White House spokesman Josh Earnest reported on April 21, the “principal goal of this operation is to maintain freedom of navigation and free flow of commerce in the Gulf of Aden and the Red Sea…this is a clear statement about our commitment to ensuring the free flow of commerce in this important region of the world.”

The Iranians recognize Obama has a tendency to declare “retractable” red lines. Iran’s actions in seizing the merchant ship Tigris is most likely yet another effort to prove to America’s regional allies they need to consider whether their own national security interests are similarly retractable by Obama.

Iranian irresponsibility in acting has given rise to U.S. irresponsibility in not acting.

Teddy Roosevelt must be rolling over in his grave.

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.