Indiana Gov. Mike Pence in an interview on Fox News Sunday. Fox News Sunday Chris Wallace challenged Indiana Gov. Mike Pence over Donald Trump's claim that he was being sarcastic when he called President Barack Obama the "founder" and "MVP" of the terrorist group ISIS.

In an interview that aired on Sunday, the "Fox News Sunday" host Chris Wallace repeatedly pressed Pence to explain why he said Trump's remarks were serious when the Republican nominee said himself that he was joking.

"You and he spent a day defending his remarks, saying that they were serious. Now Trump says that he was being sarcastic. So Governor, which is it?" Wallace asked.

The Indiana governor chalked Trump's comments up to his unorthodox campaign style, which Pence said resonated with Republican primary voters, and said Obama deserved part of the blame for allowing ISIS to fester in Syria and Iraq.

"He was making a very serious point. Donald Trump has a way of talking to get people's attention, and it's drawn attention to a very important issue," Pence said. "There was a time when a Democrat president knew where the buck stopped in the White House. And the responsibility for the failed policies in the Middle East that created the environment where ISIS developed belongs to President Barack Obama and Secretary of State Hillary Clinton, and the American people know that."

But Wallace did not let up his line of questioning, noting that Trump also claimed he was joking last month when he called on Russian hackers to find and release over 30,000 emails Hillary Clinton deleted off her private email server while serving as secretary of state.

"Those are all perfectly legitimate points to make, but that isn't what Trump said. He said that Obama and Clinton were the most valuable players of ISIS, that they were the cofounders of ISIS. Then he said, 'well, I was just being sarcastic about that,' just as he said he was just being sarcastic about inviting Russia to come in and release emails of Hillary Clinton’s," Wallace said. "Isn't the sarcastic excuse getting a bit old?"

For his part, Trump himself hasn't clarified whether his comments were serious or a joke.

During a rally in Pennsylvania on Friday, the real-estate magnate appeared to walk back his assertion that he was being sarcastic.

"So I said, the founder of ISIS. Obviously, I’m being sarcastic," Trump said. "But not that sarcastic, to be honest with you."