Former Vice President Kamala Harris was angry over former President Biden donning a Trump 2024 hat during an event in September 2024, which quickly went viral on social media at the time, according to Jake Tapper and Alex Thompson's new book. 

"What is he doing?" the former vice president asked her team in response to the video, according to the book. "This is completely unhelpful. And so unnecessary."

A video of the former president donning a Trump 2024 hat went viral in September 2024. A video of Biden at the Shanksville Fire Station in Pennsylvania showed the president taking the Trump 2024 campaign hat from a Trump supporter and putting it on top of his own hat, in what the White House said at the time was a friendly gesture of unity.

According to the book, "Original Sin: President Biden’s Decline, Its Cover-up, and His Disastrous Choice to Run Again," that was the last time Harris would do a public event with Biden prior to the election.