A day earlier, he told a radio host that Obama deserves blame for the Muslim terror group's rise because of the US military withdrawal from Iraq in 2011, which left a power vacuum for the terror group to exploit.
"He was the founder. The way he got out of Iraq ... that was the founding of ISIS, OK?" Trump said on Hugh Hewitt's radio show Thursday morning.
Of course, a distinction can be drawn between the actual founding of ISIS and its rise to the murderous, land-holding terror force that it is today. So how did ISIS begin and evolve? Here's a refresher:
The group's roots are in the Sunni terror group al Qaeda in Iraq (AQI), started in 2004 by Jordanian Islamist Abu Musab al-Zarqawi. It was a major player in the insurgency against the US-led forces that toppled Saddam Hussein in 2003, and against the Shiite-dominated government that eventually replaced Hussein.
ISIS has also targeted the Shiite community in general, starting with a deadly suicide bombing at a mosque in Samarra in 2006.
It exploited Sunni resentment against Shiites
Hussein had led a secular government, but it was dominated by members of Iraq's Sunni minority and it brutally repressed opposition. When Saddam was ousted, power went to the majority Shiites, who wanted revenge.
There was a growing perception among Sunnis that they were being persecuted and excluded from power by Shiite officials.
AQI recruited Sunni fighters to its cause -- trying to establish a Sunni Islamist control of the country.
It was rebranded, and then was largely defeated
After Zarqawi was killed in a US airstrike in 2006, Egyptian Abu Ayyub al-Masri took over and announced the creation of the Islamic State in Iraq. (The words "and Syria" would come later.)
By 2006, ISI controlled much of western Iraq's Anbar province. But then in 2008, a surge of US troops, with the help of Sunni tribesmen who were at odds with al Qaeda, largely defeated the group in Iraq.
It picked up a new leader and a new fight -- in Syria
Masri was killed in a 2010 US-Iraqi operation. That opened the door to
Abu Bakr al-Baghdadi, a militant who'd joined previously.
Baghdadi took over the group, and when a civil war kicked off in neighboring Syria, members of the group went there to fight against Syria's government forces.
It took territory, and a new name: ISIS
After ISI's forces gained strength in Syria, it re-entered Iraq in 2013 "as a reinvigorated force ... seizing much of Anbar a year later," CNN national security analyst Peter Bergen wrote earlier this year
That year, Baghdadi announced the group would be known as the Islamic State in Iraq and Syria (ISIS). He also said he was merging his force with the al Qaeda-affiliated group Al-Nusra Front -- which didn't exactly agree.
Al-Nusra Front, fighting in Syria, rejected Baghdadi's move, and in 2014, al Qaeda itself renounced its ties to ISIS after months of Nusra-ISIS infighting.
It took advantage of ex-Iraqi officers' experience
ISIS fighters got better, in part because they were being led by former officers of Saddam's army.
The United States disbanded Iraq's army in 2003 to start a new one from scratch, leaving many Sunni officers out of work. Remember the Sunni resentment against the new Shiite-led government? Some aggrieved Sunni officers joined the insurgency, and eventually ISIS.
It skillfully used prison 'networking'
By now, many of its top leaders were former inmates at US-administered prisons in Iraq during the insurgency. Those prisons, it appears, were networking centers
for those who would join the movement.
Analysts say Baghdadi and some of his top deputies were at various points imprisoned at Camp Bucca, which was a US-run prison in southern Iraq.
It took Mosul, announced a caliphate and became a major US target
In June 2014, ISIS took Mosul, a major city in northern Iraq. Later that month, Baghdadi announced the creation of a caliphate, or Islamic state. By then, ISIS had captured large swaths of Syria and Iraq.
The United States began airstrikes against ISIS targets in both countries later that year.
Retired Maj. Gen. James "Spider" Marks, a CNN military analyst, told CNN's "Erin Burnett OutFront" on Thursday that calling Obama the founder of ISIS was "crazy talk." But, he said, "clearly there's culpability."
"There's a lot we could have done in Iraq. Our departure in 2011 was premature," Marks said. "Conditions were not set. ... This (ISIS) is an organized military with a focus."