Story highlights Donald Trump insists that ISIS could not have been built without oil

"I don't call them critics. I call them fools," he said of his critics

(CNN) Donald Trump said Wednesday there would be no ISIS had the US kept Iraq's oil, following the US invasion into the country.

"We should have kept the oil when we got out. And you know, it's very interesting. Had we taken the oil, you wouldn't have ISIS, because they fuel themselves with the oil. That's where they got the money," the President told ABC's David Muir.

"We should have taken the oil. You wouldn't have ISIS if we took the oil."

Critics have said that taking Iraq's oil would have been stealing from civilians and thus a war crime, a violation of international law. The President repeatedly campaigned on bombing Iraq oil fields to keep ISIS from profiting off of oil.

"Can you believe that? Who are the critics that say that? Fools. I don't call them critics. I call them fools," Trump said.

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