(CNN) Words can change meaning over time -- especially when they are spoken by politicians. Just ask Bill Clinton to define "is."

"Literally" was once used, exclusively, to introduce or punctuate a point meant to be taken in literal terms. But by 2013, enough people were using it interchangeably with "metaphorically" that even leading grammar pedants threw up their hands (literally?), and the Merriam-Webster and Cambridge dictionaries expanded their definitions.

Donald Trump has, throughout his campaign, tested the pliability of rhetoric and language, sometimes to underline an affirmative point, but more often of late -- and in particular on Friday morning -- as a tool for walking back damaging (or straight-up false ) assertions.

On Wednesday, the Republican nominee launched a new round of criticism against President Barack Obama and Democratic nominee Hillary Clinton, the former secretary of state, calling Obama the "founder" of ISIS and Clinton its "co-founder."

Given multiple opportunities to allow that his language had been hyperbolic or, yes, metaphoric, Trump refused. On Thursday, conservative radio host Hugh Hewitt practically begged him to narrow his definition.

"Last night, you said the President was the founder of ISIS. I know what you meant," Hewitt said . "You meant that he created the vacuum, he lost the peace."

But Trump wouldn't play along.

"No, I meant he's the founder of ISIS," Trump said. "I do. He was the most valuable player. I give him the most valuable player award. I give her, too, by the way, Hillary Clinton."

Hewitt again: "But he's not sympathetic to them. He hates them. He's trying to kill them."

"I don't care," Trump said. "He was the founder. His, the way he got out of Iraq was that that was the founding of ISIS, okay?"

Sensing progress, Hewitt probed a little further, and Trump seemed to be coming around, saying that if Obama "would have done things properly (in managing the withdrawal from Iraq), you wouldn't have had ISIS."

"That's true," Hewitt said.

"Therefore," Trump added, closing the circle, "he was the founder of ISIS."

A day of furious -- if somewhat puzzled -- fact-checking followed. The reviews were unanimous. No, Obama was not the founder of ISIS. That title mostly belongs to Abu Musab Al-Zarqawi, who led al Qaeda in Iraq before being killed in an American airstrike. The group rebranded after his death, becoming ISIS, and under the guidance of Abu Bakr al-Baghdadi has capitalized on a series of missteps by both the George W. Bush and Obama administrations -- along with a civil war in Syria and Iraqi government failures -- to create a new global terror state.

By Friday morning, as the backlash to Trump's comments was again threatening to knock out the potential to generate any positive news or electoral momentum, he began a familiar process -- the walk-back.

And true to this latest narrative's grammarian nightmare theme, Trump did it with a confounding declaration.

"Ratings challenged @CNN reports so seriously that I call President Obama (and Clinton) 'the founder' of ISIS, & MVP," he tweeted. "THEY DON'T GET SARCASM?"

Ratings challenged @CNN reports so seriously that I call President Obama (and Clinton) "the founder" of ISIS, & MVP. THEY DON'T GET SARCASM? — Donald J. Trump (@realDonaldTrump) August 12, 2016

Rep. Seth Moulton, a Democrat and Iraq War veteran, was unimpressed.

"Donald Trump has shown that he lies every single day and then the next day he just tries to claim it was sarcasm," he told CNN's Brianna Keilar on "New Day."

JUST WATCHED Fact check: The real founder of ISIS Replay More Videos ... MUST WATCH Fact check: The real founder of ISIS 05:27

Former House Speaker Newt Gingrich, a close ally, said on "Fox and Friends," that "one of the things that's frustrating about (Trump's) candidacy is the imprecise language. He sometimes uses three words when he needs 10."

However, many words Trump chooses to employ, "sarcasm" -- in this case -- should not be among them.

The term is precise. The dictionaries match the vernacular. It is the use of irony, of pointedly saying the opposite of what you mean in order to make a rhetorical point.

Taken in a sarcastic light, Trump's words would be amount to a mockery of... Trump's words.

A little later Friday morning, the Republican nominee tweeted more scorn at the press.

"I love watching these poor, pathetic people (pundits) on television working so hard and so seriously to try and figure me out," he wrote. "They can't!"

I love watching these poor, pathetic people (pundits) on television working so hard and so seriously to try and figure me out. They can't! — Donald J. Trump (@realDonaldTrump) August 12, 2016

Literally true.