A day after Donald Trump repeatedly called President Obama the "founder" of the Islamic State and labeled Hillary Clinton the terrorist group's "co-founder," he shifted his tone abruptly, insisting he was being sarcastic and blaming the news media for misrepresenting his comments.

Trump's Friday remarks, delivered on Twitter and at a rally in Erie, Pa., marked an a blunt change in tone from Thursday, when he lobbed his attacks against Obama and Clinton in a serious manner during interviews and speeches. In at least one of the interviews, he was given a chance to explain whether his words carried some other meaning, and he declined to do so.

On Friday, the Republican presidential nominee argued it should have been clear that he wasn't being serious.

"So I said 'the founder of ISIS,' obviously I'm being sarcastic," Trump said at the afternoon rally in Erie, using an acronym for the Islamic State. He added: "But not that sarcastic, to be honest with you."

On Friday morning, Trump took to Twitter to accuse CNN of not understanding his remarks.

But when given a chance to explain his comments more fully in a Thursday interview with conservative talk radio host Hugh Hewitt, Trump stuck to his attack.

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

Trump responded: "No, I meant he’s the founder of ISIS. 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 noted that Obama has waged an effort against the Islamic State: "He’s not sympathetic to them. He hates them. He’s trying to kill them."

Trump responded: "I don’t care. He was the founder. His, the way he got out of Iraq was, that was the founding of ISIS."

What is now known as the Islamic State was founded by Abu Musab al-Zarqawi and was active in Iraq by 2003, when Colin Powell, secretary of state at the time, mentioned him in a United Nations speech.

Trump argued Friday that his MVP comments should have signaled that he was being sarcastic.

It's happened over and over: Donald Trump makes a controversial statement then walks it back by saying he was joking or being sarcastic. (Sarah Parnass/The Washington Post)

The nominee was introduced in Erie by Republican National Committee Chairman Reince Priebus. He plans to hold a second rally in Altoona, Pa., later Friday.

During his speech, Trump took a dig at his former GOP rivals who refuse to back him despite signing a pledge months ago to support the eventual nominee: "You know what I say to 'em: 'Get over it.'"