Donald Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE says he has lessons for a military expert who criticized his analysis of the battle to retake the Iraqi city of Mosul from the Islamic State in Iraq and Syria (ISIS).

“I’ve been hearing about Mosul now for three months,” he told ABC News’s George Stephanopoulos Wednesday. “'We’re going to attack, we’re going to attack.' Why do they have to say three months before the attack, ‘We’re going in?’"

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“Don’t talk about it," the Republican presidential nominee added. "[It’s the] element of surprise. So you can tell your military expert that. I’ll sit down and I’ll teach him a couple of things.”

Trump was criticizing Jeff McCausland, a retired Army colonel and former dean of the Army War College in Carlisle, Pa.

McCausland panned Trump’s opinion of the military offensive to retake Mosul from ISIS after it began last week.

“What this shows is Trump doesn’t know a damn thing about military strategy,” he said of Trump’s remarks on the Mosul campaign in a New York Times article published Oct. 20.

Iraqi Prime Minister Haider al-Abadi announced on Oct. 17 the offensive to retake Mosul from ISIS was commencing.

The commander of the U.S.-led coalition supporting Iraqi forces said the same day he expected a prolonged struggle against the terrorist organization.

“This operation to regain control of Iraq’s second largest city will likely continue for weeks, possibly longer,” Lt. Gen. Stephen Townsend said in a video statement.

Trump on Wednesday reiterated coalition forces erred by telegraphing their assault on the ISIS stronghold beforehand.

“One of the reasons they wanted Mosul, they wanted to get the ISIS leaders they thought were in Mosul,” he said. "Those people have all left. As soon as they heard they were going to be attacked, they all left. Why can’t they win first and talk later?”

ISIS captured Mosul in 2014, and shortly thereafter the group’s leader, Abu Bakr al-Baghdadi, proclaimed the birth of a self-styled caliphate from the pulpit of one of the city’s mosques.