It is becoming increasingly clear that the Islamic State is on the ropes in Iraq and Syria, and its defeat is just a matter of time.

What is less clear is whose strategy produced the victory.

This week, Secretary of State Rex Tillerson announced that the group's "fraudulent caliphate in Iraq and Syria is on the brink of being completely extinguished," and credited "an aggressive new strategy led by the president." On Thursday, U.S. and Iraqi officials announced that troops had seized control of Hawija in Iraq, the last major town held by the terror group in that country.

The president himself declared Thursday that more progress in the campaign to defeat Islamic State had been made in the last eight months than in "many, many previous years, all combined."

But former Defense Secretary Ash Carter, in a lengthy essay published by Harvard's Kennedy School of Government, argued the Trump administration is crowing about the results of what is essentially Obama's strategy, in which the U.S. would work "by, with, and through," local partners forces, providing air support and intelligence, but not doing the heavy lifting of front line combat.

"It was not possible to complete the job on President Obama's watch, but I was confident as I departed the Pentagon that I was handing to my successor a military campaign plan capable of dealing ISIS a lasting defeat," Carter wrote. "And despite a presidential promise of a ‘secret plan,' the coalition campaign under the Trump administration is largely on the same track we laid out for it over Christmas of 2015."

Two months before the election, Trump said he would give his top generals 30 days to submit a new plan to "soundly and quickly" defeat Islamic State, which he codified in a presidential memorandum a week after his inauguration.

The Pentagon dutifully delivered the preliminary framework Feb. 27, meeting the 30-day deadline. But when the final plan was made public by Defense Secretary Jim Mattis in May, it sounded a lot like the old plan, albeit with a few new wrinkles, designed to speed the defeat of Islamic State.

In a Pentagon briefing April 11, Mattis gave all the credit to Trump.

"First, he delegated authority to the right level to aggressively and in a timely manner move against enemy vulnerabilities," Mattis said. "Secondly, he directed a tactical shift from shoving ISIS out of safe locations in an attrition fight to surrounding the enemy in their strongholds so we can annihilate ISIS."

What Mattis described as a change in tactics, did not amount to a whole new strategy, but rather a major refinement of the old strategy, says retired Col. Steve Warren, a former Pentagon spokesman who is now a CNN contributor.

"It was enough of a refinement that I believe it did make a difference in the speed with which we were able to finish off ISIS in Iraq, but they were doomed anyway," Warren said. "I think they took a good strategy and they improved it. They made it better."

One former senior military commander in the region, who spoke on condition of anonymity, argues the changes were subtle, but had a profound impact.

It's true, he said, that no new strategy was put in place, but he called the "tweaks" to the old strategy "very good ones in terms of instituting more realistic rules of engagement, and greater delegation of engagement authority."

"The Obama administration had centralized tactical level decision-making in the White House to the degree that it was just as bad, if not worse, than during the Johnson administration,

à la ‘They can't bomb an outhouse in Vietnam without my permission,' " the former commander said. "The adjustments made by the Trump administration were and are welcome by the warfighters."

"The most important thing is that he gave ground commanders the flexibility they needed to fight each battle in such a way that it was more effectively fought," Warren said.

Warren, who did a tour in Iraq as the chief U.S. military spokesman in Baghdad, said Mattis' other change — insisting the Iraqis surround and annihilate ISIS instead of allowing them to run away and fight another day — also made a significant difference.

"I think the Iraqis would have been more than happy to keep on going with their ‘surround it three-quarters of the way, and leave them a way out,' because that really is their way of war," Warren said. "When Mattis got on board that was just not OK with him, and he really pushed the Iraqis to employ the annihilation technique."

The former U.S. commander criticized Obama for what he called a "gradualistic approach" with "minimal U.S. military commitment," intended to take years not months to accomplish.

So, does the Trump team get credit for doing what Obama's did not?

"They can't take credit for defeating ISIS, no," Warren argued. "They can share credit certainly, and I think they can take credit for successfully speeding up the campaign."

But it is clear the military favored the Trump approach, as evidenced by the parting comments of Lt. Gen. Stephen Townsend as he prepared to relinquish command of the counter-ISIS operation in August.

"We don't get second-guessed a lot. Our judgment here on the battlefield in the forward areas is trusted. And we don't get 20 questions with every action that happens on the battlefield and every action that we take," Townsend said. "I don't know of a commander in our armed forces that doesn't appreciate that."