Stephanie Grisham, one of former President Donald Trump's most senior and longest-serving advisers, says she is "terrified" that her former boss may run for office again.

"I am terrified of him running in 2024," Grisham, who served as both Trump's press secretary and first lady Melania Trump's chief of staff, told "Nightline" co-anchor Juju Chang in a wide-ranging exclusive interview on the eve of the publication of Grisham's new book.