Top defense officials tried to convince reporters on Thursday that the U.S. military's mission to protect oil fields in eastern Syria isn't just about the oil.

“The mission is the defeat of ISIS,” said Navy Rear Adm. William Byrne, Jr., vice director of the Joint Staff. “The securing of the oil fields is a subordinate task to that mission. The purpose of that task is to deny ISIS the revenues from that oil infrastructure.”

Let's back up for a minute. On Oct. 13, Defense Secretary Mark Esper announced that most U.S. troops were withdrawing from Syria because Turkey's invasion of Kurdish territories had gone further than expected.

Everything changed six days later when President Donald Trump tweeted that the United States had “secured the Oil” in eastern Syria, prompting the U.S. military to deploy Bradley fighting vehicles around Deir ez-Zor.

Trump has tweeted or otherwise commented since then that U.S. troops in Syria are securing the oil fields. For example, the president used the word “oil” 23 times when he announced the death of ISIS founder and former leader Abu Bakr al-Baghdadi on Oct. 27.

“The oil is, you know, so valuable for many reasons,” Trump said. “It fueled ISIS, number one. Number two, it helps the Kurds, because it's basically been taken away from the Kurds. They were able to live with that oil. And number three, it can help us because we should be able to take some also.

“And what I intend to do, perhaps, is make a deal with an Exxon Mobil or one of our great companies to go in there and do it properly. Right now, it's not big. It's big oil underground, but it's not big oil up top, and much of the machinery has been shot and dead. It's been through wars. But — and — and spread out the wealth.”

But on Thursday, defense officials insisted that protecting the Syrian oil fields was merely a means to an end, namely to keep ISIS from having an income.

To wit: All profits from the oil's sale is going to the Syrian Democratic Forces, not the United States, chief Pentagon spokesman Jonathan Hoffman said at a news briefing. The SDF are using that money to keep up operations against ISIS.

When reporters repeatedly asked what legal basis the United States has to control the Syrian oil fields, Hoffman said that Trump has the authority to order U.S. troops to protect the oil fields as part of military operations against ISIS.

“All of our operations in Syria are done under the commander in chief's authorities with regard to protecting Americans from terrorist activity including ,” said Hoffman, who accused reporters of trying to “decouple” the oil field mission from the fight against ISIS.

“Just to be clear, we've been in this area with the same mission of preventing ISIS from getting those oil fields for the last four years,” Hoffman said later in the briefing. “This is not a new mission. Everybody seems to believe that has changed. That is not the case. This authority has been in place for years and we believe it's consistent with the president's authority and the desire to prevent ISIS from obtaining funds from which to be able to conduct terrorist operations around the globe.”