Vice President Kamala Harris said that if former President Donald Trump is too “exhausted” to campaign amid a series of interview cancellations, it raises questions about his fitness for president.

At an energetic rally in Grand Rapids, Michigan, on Friday, Harris pointed out that Trump had canceled interviews just 18 days before the election.

In recent weeks, Trump has withdrawn from interviews with major media outlets, including “60 Minutes,” CNBC and NBC News. And on Thursday, the National Rifle Association announced it was canceling an event with Trump due to “changes in the campaign schedule.”

“He’s avoiding debates and canceling interviews,” Harris told the crowd in Grand Rapids. “And check that out; his own campaign team recently said it was due to exhaustion.

Harris was referring to a Politico report Friday that Trump had pulled out of an interview with the website The Shade Room and that one of his advisers had told Shade Room producers that he was “exhausted and refusing ( some) interviews, but that could change.

Waka Flocka Flame, a rapper who has been a vocal supporter of Trump, has reportedly been offered a replacement interview in place of the former president.

“Well, if you’re burned out on the campaign trail, it raises real questions about whether you’re fit for the toughest job in the world,” Harris said to applause. “Come on. Come on.”

Asked about Harris’ comments, Trump told reporters Friday that he wasn’t exhausted, called the vice president a “loser” and lied about not going to events.

“Which event did I cancel?” I didn’t cancel,” Trump said. “She’s not going to any events, she’s a loser, she’s not going to any events.”

Trump pointed out that he attended Al Smith’s charity dinner in New York on Thursday, where he complained about not being able to use a teleprompter. Trump also made an appearance on “Fox & Friends” Friday morning where he responded to a 6-year-old boy’s question about his favorite animal by absurdly suggesting that Harris would get rid of cows if elected.

“I love cows. But if we go with Kamala, you won’t have any more cows,” Trump told the child.

Speaking to reporters, Trump said that after his appearance on Fox, he “made about 15 calls.”

“I went 48 days without rest and I have this loser who doesn’t have the energy of a rabbit,” he said.

“Tell me when you saw me take even a little rest,” Trump added. “I’m not even tired, I’m really elated.”