DONALD TRUMP’S ENERGY levels emerged as a flashpoint in the presidential race as the Republican nominee and Democrat Kamala Harris scrambled across battleground Michigan with election day looming.

Harris told reporters that Trump was “unfit”, “unstable” and “a danger to our democracy” ahead of an afternoon rally.

But she appeared to touch a nerve with her Republican rival when she mentioned a report that Trump was “exhausted”.

“Being president of the United States is probably one of the hardest jobs in the world and we really do need to ask, if he’s exhausted on the campaign trail, is he fit to do the job?” said Ms Harris, who has been on the road campaigning since Monday and will not return to Washington until some time next week.

Her attack comes as she seeks to raise doubts about Trump’s health over the final days of the campaign.

Trump, at 78, would be the oldest person in US history to become president if he wins. But he has refused to release his medical records or other health details, breaking decades of tradition in presidential politics.

Trump, who has been campaigning at a breakneck pace as well, fired back later in the day when asked by reporters about Ms Harris’ comment.

“She’s a loser. She doesn’t go to any events,” Trump said, hours before a rally in Detroit as he ticked down his to-do list for the day.

He said he was on Fox & Friends at 7am, had two other appearances and then made “about 15 phone calls”.

“I’ve gone 48 days now without a rest. And I’ve got that loser, who doesn’t have the energy of a rabbit,” Trump said.

“Tell me when you’ve seen me take even a little bit of a rest. Not only am I not, I’m not even tired. I’m really exhilarated.”

Questions about Trump’s energy levels come as he has backed out of some interviews with mainstream media outlets, including 60 Minutes and CNBC.

Still, he appears regularly on friendly cable shows and conservative podcasts, often sitting for hours of interviews each day.

Yesterday, he spent 40 minutes on set with the hosts of Fox & Friends before he joined The Dan Bongino Show, a video podcast, and taped an interview with Mark Calaway, the wrestler famously known as The Undertaker, for his Six Feet Under podcast.

He also attended an editorial meeting with Fox News and the New York Post before he left for a multi-stop trip to Michigan.

Still, leading Democrats, including top Harris campaign adviser David Plouffe, continue to raise questions about Trump’s energy levels.

“This is important,” Plouffe said on CNN.

“I’ve worked in the White House. It’s the hardest job in the world, and I think it raises real questions.

“If somebody can’t handle the campaign trail because they’re so exhausted, whether they’re fit to be president. You just have to watch him every day.”