Army Chief of Staff Gen. Raymond T. Odierno said Wednesday that he disagrees with Republican presidential candidate Donald Trump’s idea that the United States should go into Iraq and seize oil being used to fund the Islamic State militant group, saying that there are limits on what military power can do.

Odierno’s comments came in a wide-ranging briefing with reporters at the Pentagon as he prepares to retire as the Army’s top officer after 39 years of service. Trump, the Republican front-runner in the 2016 presidential election, said Tuesday in a television interview that he “would go in and take the oil” and put troops in place to protect the oilfields.

“Go and take the money source away,” Trump said on CNN. “Believe me, they would start to wither, and they would collapse.”

Odierno, who served as the top U.S. commander in Iraq from September 2008 until September 2010, was asked directly about the remarks Wednesday, and noted previous problems with using military force without coordinating with governments in the Middle East.

“The problem we’ve had is we’ve had outcomes, but they’ve been only short-term outcomes because we haven’t properly looked at the political and economic side of it,” the general said Wednesday. “It has got to be three that come together. And if you don’t do that, it will not solve the problem, and that is what I continue to look at.”

Odierno added that if the Islamic State posed an imminent threat of launching a devastating attack, he would look at things differently.

“That is not where we are today,” he said. “What we want to do is try to stop… a group that is potentially attempting to be a long-term influence in the Middle East, that is clearly promoting extremism and frankly suppressing populations in the Middle East. In order to resolve that, you need countries of the Middle East and those surrounding the Middle East to be involved in the solution.”

Asked if that means he disagrees with Trump, Odierno answered directly: “I do, I do. Right now, I do.”

The Islamic State gains some of its money from oil fields in Iraq and Syria, but other financing come through extortion, taxing people and the sale of looted antiquities, according to a Congressional Research Service report released in April. The oil the Islamic State does sell moves through the Turkish border, and at a reduced price.

Odierno said that he believes the United States is at “an inflection point” regarding national security. He listed a variety of concerns, including Russian aggression in eastern Europe, Chinese aggression in the Pacific, the uncertain future of Afghanistan, the use of terrorism across the world and the provocative actions of North Korea.

“There’s a lot of issues out there, and I didn’t name them all,” he said. “Those are the major ones.”

Odierno also said Wednesday that the Army will likely continue its assessment of women at Ranger School by holding another gender-integrated course beginning in November. The remainder of the first class to include women began in April, with two women now in its final phase at Eglin Air Force Base in Florida potentially becoming the first female service members to complete the course.

“I don’t know how it’s going to come out, because you never know,” Odierno said of women possibly graduating. “There’s several days left yet in Ranger School. But the feedback I’ve gotten with these women is how incredibly prepared they are. The effort that they’ve put forward has been significant. They’ve impressed all that they’ve come in contact with. They are clearly motivated and — and frankly, that’s what we want out of our soldiers.”

A decision is coming soon on whether to allow women in infantry and armor units, he added.