'You don't know what to expect': Trump outlines his biggest challenge in debating Harris

PHILADELPHIA — Former President Donald Trump said that the biggest challenge in debating Vice President Kamala Harris Tuesday night will be the fact that over the years, she's shifted her positions on so many issues.

"You don't know what to expect. She's changed all of her policies over the years," Trump told NBC News in phone interview Tuesday morning.

He added, however, that he believes it makes it "easier" to define her in the minds of voters.

"It makes it much easier. She's no longer believable," Trump said.

The debate here Tuesday night, sponsored by ABC, is Trump's second of the 2024 election — but his first against his new opponent. It's Harris' first general election debate as a presidential candidate ever.

Trump enters debate day feeling — in his words — "great." The former president's debate preparations have been far less extensive and structured than what Harris has been doing, but he participated in extensive sessions over the past two days, according to a source familiar.

Three sources who speak to Trump regularly, including one directly involved in the debate prep process, described Trump as either nervous or disengaged with debate preparation in the past few weeks. But that changed as the debate grew closer, and he's been much more dialed in.

The three sources — who requested anonymity to describe private conversations with the candidate and his team — said that he is in a much more focused head space Tuesday than he has been in recent days — with two suggesting that favorable public polling have helped. 

Two of the sources said that that the Trump strategy will not be to paint Harris as a flip-flopper, but rather to take her most liberal past position and make her own it. One person pointed to comments by Sen. Bernie Sanders, I-Vt., as a road map. On Sunday, he went on NBC News' "Meet the Press" that Harris is a progressive but “doing what she thinks is right in order to win the election."

Trump, too, has frequently shifted his positions over the years, including on issues like abortion and TikTok.

Harris, for her part, will try to "remind people of what it was like during Donald Trump’s years," according to a source familiar with her debate strategy.

Her team had unsuccessfully pushed to have the candidates' microphones on the whole time. But even with the microphones muted while the other person is speaking, they're preparing for unscripted and potentially volatile moments — including the possibility that Trump makes derogatory comments about her, according to sources familiar with her preparations.

The Harris campaign did not immediately return a request for comment.