Donald Trump claims he could teach the former dean of the Army War College 'a couple of things' after the military expert said the billionaire 'doesn't know a damn thing about military strategy.'

The Republican candidate tweeted on Sunday that the ongoing operation against ISIS in the terrorist stronghold of Mosul in northern Iraq was a 'total disaster.'

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

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Donald Trump claims he could teach the former dean of the Army War College 'a couple of things'

The Republican candidate tweeted on Sunday that the ongoing operation against ISIS in the terrorist stronghold of Mosul in northern Iraq was a 'total disaster'

Jeff McCausland, the former dean of the Army War College, had criticized Trump after the tweet claiming it showed that the real estate mogul's lack of understanding about military strategy.

'What this shows is Trump doesn't know a damn thing about military strategy,' he said.

During an interview with ABC's George Stephanopoulos, the Donald said he could teach the retired U.S. Army colonel, who was a director for defense on the National Security Council during the Kosovo crisis, a few things about military strategy.

Jeff McCausland, the former dean of the Army War College, had criticized Trump after the tweet

'You can tell your military expert that I'll sit down and I'll teach him a couple of things,' Trump said.

'The element of surprise,' he announced as his own suggestion for a better 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. Okay? We're going to attack. Why do they have to talk about it?'

Trump blamed Hillary Clinton and President Barack Obama - who he has previously called the founders of ISIS, as the reasons why the U.S. 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.

He even claimed that if he had been president in 2004, he could have prevented some of the tragic losses the U.S. military, and the families of service men and women, have suffered.

That includes the death of Captain Humayun Khan who died in combat in Iraq.

'Had I been president, Captain Khan would be alive today,' Trump said, 'because I wouldn't have been in Iraq. We wouldn't have been in this horrible, horrible mistake, the war in Iraq.'

Trump claimed that if he had been president in 2004, he could have prevented the loss of Khizr Khan's (pictured) son Captain Humayun Khan who died in combat in Iraq

The Iraqi army's retaking of Al Qayyarah town from ISIS during the operation to retake Iraq's Mosul

Trump has made regular assertions during his campaign - without any evidence - that he was against the war in Iraq from the start.

Capt. Khan's father, Khizr, who is out on the campaign trail with Clinton today, shot back after hearing Trump's comments, saying: 'This is the most cruel thing you can say to grieving parents, that if I was there this would not have happened.'

Khizr Khan first gained national attention from the podium of the Democratic National Convention when he paid homage to his son. Khan had held up his pocket-sized Constitution and said Trump has sacrificed 'nothing.'

Trump later outraged many Republicans when he responded by attacking Khan's sincerity, suggesting that Clinton's speechwriters scripted his speech. He also claims that Khan's wife, who stood with her husband at the podium probably wasn't allowed to speak to him.

Khan is now back on the campaign trail with Clinton and has appeared in a new advert where he challenges Trump: 'Would my son have a place in your America?'

During an interview with ABC's George Stephanopoulos, the Donald said he could teach Jeff McCausland, a few things about military strategy

He added he believed that the ISIS leaders who the U.S. and its allies had been targeting have left Mosul after they announced they were going in.

'As soon as they heard they're gonna 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?'

However, the people on the ground disagree with Trump.

Defense Secretary Ash Carter, who is currently in Iraq, said that the U.S. military were making progress against ISIS and the battle was 'going according to plan.'