Republican National Committee Chair Ronna McDaniel said that Donald Trump, the frontrunner in the GOP presidential race, would be making “a mistake” if he opts out of the upcoming primary debate.

“I think it’s a mistake not to do the debates, but that’s going to be up to him and his campaign,” McDaniel told Fox News on Wednesday.

Trump has thrown cold water on the idea of taking the debate stage on Aug. 23 in Milwaukee, citing his large lead in the polls over the other Republican candidates.

“When you have a big lead, you don’t do it,” Trump said during an interview on Fox News Sunday, adding, “I haven’t really made up my mind.”

McDaniel also said she has tried to convince Trump to commit to joining his competitors on stage, but to no avail. Still, she laid out the case for why she thinks he’d be missing out.

“You want to win the nomination, you got to get in front of those primary voters. But for me, it’s another part of it … this is an audience of 20 million people, plus,” she said. “Leaving that opportunity aside and not getting on the debate stage is just more of an opportunity for Joe Biden to continue to get his message out.”