Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE took aim at Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE on Twitter Tuesday, mocking her for not campaigning and saying she “needs her rest.”

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“Hillary Clinton is taking the day off again, she needs the rest. Sleep well Hillary - see you at the debate!” Trump tweeted.

Hillary Clinton is taking the day off again, she needs the rest. Sleep well Hillary - see you at the debate! — Donald J. Trump (@realDonaldTrump) September 20, 2016

Trump, the Republican presidential nominee, has been taking subtle shots at Clinton’s stamina throughout the presidential campaign, claiming the demands of the White House would be too much for her.

Trump on Tuesday also accused Clinton, the Democratic nominee, of imitating his signature “airplane rallies.”

“Do people notice Hillary is copying my airplane rallies - she puts the plane behind her like I have been doing from the beginning,” he wrote in a tweet.

Do people notice Hillary is copying my airplane rallies - she puts the plane behind her like I have been doing from the beginning. — Donald J. Trump (@realDonaldTrump) September 20, 2016

Clinton has held several press conferences in recent weeks on airport tarmacs, often in front of her campaign plane.

She spoke to reporters on Monday on the tarmac at an airport in White Plains, N.Y., addressing the recent bombings in New York and New Jersey and the stabbings in Minnesota.

"The facts are pretty clear. We still have challenges. That's what I have been talking about throughout this campaign. I am prepared and ready to actually take on those challenges," she said.

"You don't hear a plan from [Trump]. He keeps saying he has a secret plan. Well, the secret is he has no plan."