WASHINGTON ― President Donald Trump may be on the brink of sparking a full-blown famine in Yemen ― all because of a subtle shift in messaging that risks effectively cutting off humanitarian relief to the war-torn nation.

For more than a year, former President Barack Obama’s administration urged a coalition led by Saudi Arabia and the United Arab Emirates not to attack or seize the critical port of Hodeidah on Yemen’s west coast. The bulk of humanitarian supplies that enter Yemen flow through Hodeidah, and attacking the port, which is controlled by the Houthi rebels, would likely put it out of commission, the Obama administration warned.

But now the coalition, allied with the nominal Yemeni government of President Abdu Rabbu Mansour Hadi, has been redirecting humanitarian and commercial ships carrying food away from the Hodeidah port, relief workers told The Huffington Post. That redirection is itself a major blow to relief efforts. But it could also signal an attack is imminent.

For the past several weeks, the coalition has sent ships instead to the smaller port in Aden, about 250 miles away, said Jamie McGoldrick, a humanitarian coordinator for the United Nations. Humanitarian workers in Yemen have observed a “drastic decrease” in the number of ships reaching the port of Hodeidah,” said Christophe Morard, a logistics officer at the U.N. World Food Program, which heads a group of nonprofits working together in Yemen.

The rerouting of ships coincides with coalition airstrikes over Hodeidah and a military offensive by the Saudi-led forces to retake Mokha, another port city about 100 miles to the south. That confluence of events has led aid workers to develop a contingency plan in case the coalition moves on from Mokha and closes Hodeidah in an attempt to retake it from the Houthis, Morard said.

“Clearly they have some plans militarily for the port,” McGoldrick said of the coalition. “It’s part and parcel of an attempt to try and weaponize the economy.”

An effort by the Hadi-aligned coalition to retake Hodeidah would likely shut the port down for an extended period of time, former U.S. government officials and current aid workers say. Even a short-term halt of the flow of goods through Hodeidah would cut off life-saving food aid to Yemenis on the brink of starvation.

The Obama administration, which faced criticism from human rights groups for its military support to the Saudi-led coalition, took a hardline stance against the coalition attacking the Red Sea ports ― especially Hodeidah, four current and former administration officials told HuffPost. Obama specifically pressed the issue when Saudi Arabia’s King Salman visited the White House in 2015.

Even in a best-case scenario in which the coalition successfully retook the port from the Houthis, the battle would create front lines around Hodeidah, and there’s ample reason to believe the Houthis would make repeated attempts to reclaim it. “The passage of food through those lines would be as difficult as the passage through any other battles lines,” one former senior administration official who worked on the region said, pointing to the southern port city of Aden as an example. When the coalition retook Aden in 2015, the port was inaccessible to humanitarian aid for four months, the BBC reported at the time.

Because the Houthis control major population centers in the western part of the country, it’s unclear whether the coalition would be able or willing to distribute humanitarian aid throughout Yemen if it succeeded in taking over Hodeidah. “If we see a scenario where the bulk of the population is under the control of one side ― regardless of which side ― and the main channel for bringing in aid and commercial food is controlled by the other side, that’s a recipe for disaster,” said a second former administration official.

European Council on Foreign Affairs A map of Yemen showing Houthi control as of December 2016.

Despite pressure from the Obama administration, the coalition didn’t always leave the Red Sea ports alone.

“I don’t really know if there was much of a leash in the Obama administration,” said Sen. Chris Murphy (D-Conn.), a member of the Senate foreign relations committee. “We kept telling them not to bomb civilians, not double tap civilian targets, and they kept doing it. I’m not sure we had much control over what the Saudis and Emirates were doing before the Trump administration took over.”

Airstrikes in 2015 destroyed some of the cranes that were used to haul cargo off the ships. Last year, the coalition bombed the main bridge that connects Hodeidah to Sanaa, Yemen’s capital ― a target that the U.S. had included on a no-strike list. Efforts by the Obama administration to investigate war crimes under its watch were often half-hearted at best.

At the same time, the Saudi-led coalition, which is dependent on the U.S. for military support and diplomatic cover in its fight against the Houthis in Yemen, took objections from Washington into account. “When we saw decreases in the flow of food and medicine, we would immediately respond and you would generally see an improvement in the amounts going through,” the first former official said. “But it was something we constantly monitored.”

The State Department declined to comment on whether its position on the coalition retaking Hodeidah had changed under the Trump administration. The White House did not respond to a request for comment. But a softening of pressure from Washington on the coalition could prompt them to move forward with an operation to retake Hodeidah, current and former officials said ― and the Trump administration appears to be doing nothing to stop them.

UAE Ambassador Yousef al Otaiba, whose country has been pushing to take the port, has seen his star rise with the election of Trump. Since June, he has been mentoring White House adviser and Trump son-in-law Jared Kushner on Middle East policy.

On Thursday, Secretary of State Rex Tillerson met with the U.N. special envoy for Yemen and his counterparts from Saudi Arabia, the United Arab Emirates, Oman and the U.K. to discuss the conflict. The State Department’s readout on the meeting referenced the U.N.-led process to end the conflict and the need for the unfettered delivery of humanitarian aid. Conspicuously absent from the readout was any mention, as was included in past statements, of the need for a ceasefire in Yemen. State Department readouts are carefully parsed word for word by a team of experts who are cognizant that even a slight change in phrasing can send a meaningful signal.

The Famine Early Warning Systems Network tracks food scarcity worldwide with a one through five scale. Phase five is a famine. Between 7 and 10 million people in Yemen are estimated to be in phase three, the crisis phase. Of that population, at least 2 million are in phase four, the emergency phase.

Stringer/AFP/Getty Images Saida Ahmad Baghili, an 18-year-old Yememi woman in Hodeidah. The city has already been hit hard by food scarcity. The closure of the port would exacerbate an already fragile situation.

“If there were a serious disruption to that port, that would, I think, be sufficient to tip the country into famine,” said Jeremy Konyndyk, who was the director of foreign disaster assistance at the U.S. Agency for International Development until last month. “If they were to cut off Hodeidah, you could see several governorates in Yemen possibly tip into famine,” echoed the first former official.

McGoldrick, the U.N. humanitarian coordinator, described Hodeidah as the “lifeline we use to supply 80 percent of the humanitarian needs in the country.” The other 20 percent comes in through Aden, he said. But Aden, which wasn’t built to serve the entire country, is smaller in size than Hodeidah and geographically removed from most of Yemen’s population.

“We are currently being blamed for the human misery inside Yemen, and conditions there are radicalizing Yemenis against the United States,” Murphy said. “Our policy should be to try to abate the human misery, not take steps that would increase it. That’s bad from a moral perspective, but also really bad from a national security perspective. Anything that increases the humanitarian disaster that’s unfolding in Yemen is really bad for America.”

The coalition did not respond to multiple requests for comment made through several channels. But it has defended military operations around the Red Sea ports in the past by accusing the Houthis of smuggling weapons from Iran in through the port and blocking the flow of aid.

McGoldrick denied that there is any “mass diversion” of humanitarian aid by the Houthis and said the part of the Red Sea leading to the port is “one of the most policed stretches of water in this part of the world.”

“A lot of our inability to bring goods in through Hodeidah has been blocked by the Saudi coalition,” McGoldrick said. “They control the shipping lines. They control what boats come in.”

There have always been factions within the State Department who wanted to give Saudi Arabia and the UAE a freer hand to fight the war against the Houthis. Trump’s regular verbal attacks on Iran, which helps arm the Houthis, have emboldened those in the State Department who wanted that firmer line.

If the coalition succeeded in gaining control of Hodeidah, repaired the damaged infrastructure, and prioritized bringing humanitarian assistance through the port, “it could actually be a very positive development” in the conflict, former ambassador to Yemen Gerald Feierstein argued. “But all of those are question marks,” he added.

Anti-Iran hardliners see the war against the Houthis as a proxy war against Iran, but U.S. intelligence agencies intercepted communications showing that Iran actually urged the Houthis not to launch the war. Once the conflict started, however, Iran has been happy to supply weapons to the Houthis, in order to cause problems for their rival in the region, Saudi Arabia.

Current and former administration officials said that during the Obama administration there were some in the State Department who did not object to the Saudi-led coalition attempting to retake Hodeidah and other Red Sea ports. They believed that losing the port (and the revenue that comes with operating it) could bring the Houthis to a more “amenable negotiating posture,” the second former official said. It could come, however, at the cost of mass starvation.

Others in the previous administration were skeptical of that line of logic. “The coalition’s been bombing the hell out of that country for two solid years now,” the second former official said. “Every advancement by the coalition was supposed to be the game changer that would bring the Houthis to the table. [They said] losing Aden would be a game changer that would bring the Houthis to the table ― but it didn’t change their posture much.”

“There are people who may think that this is a way to end the war quickly,” the first former official said. “That’s fiction.”