Donald Trump Says He'll Teach Military Expert 'a Couple of Things' About Mosul Trump revealed details about his plan to ABC's George Stephanopoulos.

 -- Donald Trump went on the offensive against a military expert and former dean of the Army War College, Jeff McCausland, who said the Republican nominee’s comments this weekend about the battle to reclaim Mosul in Iraq show he doesn’t have a firm grasp of military strategy.

“You can tell your military expert that I’ll sit down and I’ll teach him a couple of things,” Trump told ABC’s George Stephanopoulos in an exclusive interview.

On Sunday, Trump tweeted that the ongoing offensive against the ISIS stronghold of Mosul is turning out to be a “total disaster.”

“We gave them months of notice. U.S. is looking so dumb. VOTE TRUMP and WIN AGAIN!” he tweeted.

Trump doubled down on his assertion that the element of surprise is an important military strategy.

“I’ve been hearing about Mosul now for three months. ‘We’re going to attack. We’re going to attack.’ Meaning Iraq’s going to attack but with us. OK? We’re going to attack. Why do they have to talk about it?” he asked Stephanopoulos.

“Element of surprise. One of the reasons they wanted Mosul, they wanted to get ISIS leaders who they thought were, you know, in Mosul. Those people have all left. As soon as they heard they’re going to be attacked, they left,” Trump added. “The resistance is much greater now because they knew about the attack. Why can’t they win first and talk later?”

But according to The New York Times, some military experts disagree with Trump’s claims that the element of surprise is crucial to win the fight against ISIS.

“What this shows is Trump doesn’t know a damn thing about military strategy,” McCausland told the Times.

McCausland replied to Trump's comments to Stephanopoulos in a lengthy statement today, saying, “I can’t wait to sit down with Mr. Trump and hear what he has to teach me about military strategy. I’m happy to compare my record of over 45 years working in national security affairs with his any time.

"When it comes to the question of the Mosul offensive, Mr. Trump doesn’t understand that 99.9 percent of the troops involved are Iraqi," McCausland continued. "I reassert my statement to The New York Times: Mr. Trump doesn’t know a damn thing about military strategy.”

Democratic presidential nominee Hillary Clinton also hit Trump for his comments to Stephanopoulos yesterday at a joint campaign event with First Lady Michelle Obama in Winston-Salem, North Carolina, today.

"And yesterday when he heard a retired army colonel and former dean of the Army War College said that Donald doesn't understand military strategy, Trump said 'I'll teach him a couple of things,'" she continued. "Well, actually, Donald, you're the one who's got a lot to learn about the military and everything else that makes America great.”

Defense Secretary Ash Carter is on the ground in Iraq and told ABC’s Martha Raddatz in an interview earlier this week that he’s “encouraged” by the progress in the fight against ISIS because it “is going according to plan ... ISIL will surely be destroyed.”

Trump blamed Clinton and President Barack Obama for the need to reclaim Mosul.

“We had Mosul. We have to take it because Hillary Clinton and Obama left that big vacuum, and ISIS went in, and they took Mosul,” he said.